Can't do that myself, that'd require an Admin to separate the forums. I guess the same effect could be done with thread titles, such as:

XP: I don't get the new scripting system
2k3: Alex charset = cool
2k3: Error involving virus.dll
XP: My processor is made of meat and thus cannot play this game
2k3: WHERE I FIND GAME
XP: What's up with the lack of Alex I demand to know
XP: Hey this game has the same name as my Windows