I have the install & patch (including the multimedia patch) installed on my XP machine, and a friend has the install and all patches (including multimedia & the Vista patch) installed.  Both games read "Version 1.1" in the options window.  However, when we try to do multiplayer, we get the message stating we have different versions.  Please tell me there is a workaround for this problem, because after trying to get the game up and running on the Vista machine, (which does wonderfully now), we cannot play together.  n a whim, I've installed the Vista fix on the XP machine, without any consequences, but it didn't fix the problem either.
Thanks for your help!

You have to use the same Vista patch on your XP Version I guess.... even if you don't need it. Just give it a try but I think the Vista patch is causing different versions. I never tried to use the Vista patch on my XP machine though. It should work.