When I was setting up multi-user iTunes on my new Windows Vista box, I also came across the need to set up Picasa for multi-user support. Like iTunes, Picasa is really a single-user application so you have to do some special work to get it to share a single library across different user accounts.

Fortunately, you can use many of the same principles as in multi-user iTunes to get Picasa up and running without much issue. (Enough so that I can do some pretty easy copy/paste modification to the iTunes instructions and get Picasa instructions.)

IMPORTANT NOTES:

• This is all at your own risk.  If it doesn’t work for you, I’m sorry, but I can’t offer individual support.
• You may not be able to follow this verbatim. If these steps don’t work precisely, I recommend looking at the intent of the steps - putting the Picasa library in a central location and creating links to it from individual user profiles - and adjusting things according to your setup.
• As new versions of Picasa, Windows, etc. come out, I may not always update or catch all the little “gotchas.” I originally wrote these for Picasa 2.7… things change, versions change, OSes change, and I can’t keep these up to date for every possible combination of software.
• You must have Administrator privileges to set this up. You don’t need Admin rights once you’ve got it set up, but some of the stuff you do here needs to be run as Administrator, so make sure you can do that.
• You need to be comfortable at a command prompt. If you’re not, this may be very frustrating for you.

Now… here’s how to get it running:

1. Get the required tools. You’ll need a tool that allows you to make symbolic directory links.
   • On Windows Vista, this is built in - the mklink command.
   • On Windows XP, you need to go to SysInternals and download a copy of “junction” if you don’t already have it and put it somewhere in your path (like the C:\WINDOWS\System32 folder); you’re going to need to use it from the command prompt later.
2. Make sure everyone runs Picasa once. For each user you want to set up, make sure they’ve run Picasa at least once so they’ve accepted the EULA and Picasa has created their initial/empty library file. You’ll also be asked to set up “watched directories” when Picasa runs the first time. I recommend watching as few directories as possible and adding them in later once you’ve finished getting everyone on board.
3. Choose the Picasa library you want to share. Decide which user’s Picasa library you want to be the main one that everyone else will share. You’ll be manipulating this library. I will call it “the main Picasa library” from now on so you know what I’m talking about.
4. [Optional] Consolidate/move the main Picasa library pictures into a shared location. Picasa allows you to backup and restore pictures using its built-in tools. You can back up from one place and restore to a different place, effectively moving your library. (I will not walk you through this. It’s sort of a pain, but if you search the Picasa forums you’ll find info.) Basically: run the backup, move your original photos out somewhere else, restore the backup to a different/new location, verify you can still see things in Picasa, and delete the original photos.  Doing this will save you a lot of headache when you find that one user can’t access all the pictures that another user can due to security restrictions. Move the pictures into a shared location (like create a folder called  C:\Users\Public\Pictures\My Pictures in Vista or the C:\Documents and Settings\All Users\Documents\My Pictures\My Pictures in XP and move it there). Note that you may need to try the “restore” operation a few times before you get it the way you like it. Don’t delete your originals until you’re sure the backup restored all of the stuff you want. I am not responsible if you lose data trying this. Do it at your own risk.
5. Find the main Picasa library. The Picasa library for each user is stored across two folders inside each user’s application data folder. Both of these are part of the library, so when you’re working with the library, copy them at the same time and keep them together.
   • In Windows XP, these folders are:
     • C:\Documents and Settings\username\Local Settings\Application Data\Google\Picasa2
     • C:\Documents and Settings\username\Local Settings\Application Data\Google\Picasa2Albums
   • In Windows Vista, these folders are:
     • C:\Users\username\AppData\Local\Google\Picasa2
     • C:\Users\username\AppData\Local\Google\Picasa2Albums
6. Back up the main Picasa library. Copy the main Picasa library folders somewhere safe for backup purposes. Just in case something goes wrong.
7. Create a shared Picasa library folder. Create a new Picasa folder that all users have access to. I recommend putting it in the “Public” or “All Users” areas so you don’t have to worry about security issues. It should be something like this:
   • In Windows XP, this will be C:\Documents and Settings\All Users\Documents\My Pictures\Picasa Library.
   • In Windows Vista, this will be C:\Users\Public\Pictures\Picasa Library.
8. Copy the main Picasa library folders into the shared Picasa library folder. As simple as drag and drop - copy the two folders that make up the Picasa library into the new shared library folder you just created.
9. Create symbolic links to the shared Picasa library folders. You’re logged in as Administrator (or otherwise have Administrator rights), right? Here’s where you really need them.
   • Open a command prompt. In the Start -> Run box, type cmd and hit Enter. A command prompt should pop up.
   • For each user who needs to share the Picasa library…
     • Change to the user’s local settings folder.
       • In Windows XP: cd "\Documents and Settings\username\Local Settings\Application Data\Google"
       • In Windows Vista: cd "\Users\username\AppData\Local\Google"
     • Delete the old Picasa library folders and all of their contents. (This is why you backed the main library up earlier.) rmdir /s Picasa2 rmdir /s Picasa2Albums
     • Make a symbolic link to the new shared Picasa folders. This will replace the old Picasa folders and will “fake out” Picasa so it thinks it’s talking to a local user’s library.
       • In Windows XP: junction Picasa2 "C:\Documents and Settings\All Users\Documents\My Pictures\Picasa Library\Picasa2" junction Picasa2Albums "C:\Documents and Settings\All Users\Documents\My Pictures\Picasa Library\Picasa2Albums"
       • In Windows Vista: mklink /d Picasa2 "C:\Users\Public\Pictures\Picasa Library\Picasa2" mklink /d Picasa2Albums "C:\Users\Public\Pictures\Picasa Library\Picasa2Albums"
10. Verify the settings by logging each user in. Everyone you just set up should now be working off of the same Picasa library. Have each user who’s sharing log in and verify they can see the shared library. Do not use “Switch Users” - you must fully log off each user and log the next one on. They will all have to set up their own preferences (like their email settings, etc.) but they will all have access to the same picture library and the same albums.
11. [Optional] Update watched folder settings for each user. You may need to set up each user account to watch the same folders, and make sure each user isn’t watching their own personal “Pictures” folder. You only want Picasa to watch folders that every user sharing the library has access to, otherwise you could run into access issues.
12. That’s it! You’re done!

I’ve had this running for a couple of weeks now and haven’t had any issues. The toughest part really is doing the backup/restore to move your pictures to a new location that everyone can access. Just be patient with it and be willing to spend the time it takes to try it a few times. Oh, and be sure to back things up and verify your changes take hold before you delete things. You’ll get it. It’s not that bad.

All instructions here are provided for your UNSUPPORTED use and AT YOUR OWN RISK.