Hmm...maybe this is one of the WinXP restrictions...
I've tried to mount the folders as B: floppy (which I don't have) and it worked!!!
Well, I guess it's a partial solution of my problem, but I know that some of the games won't install from B: floppy. Oh well...thanks for the inspiration Space.

If it wasn't for you I would never try to make a virtual B: drive.
Yet, I can assure you that I could make a virtual A: on Win98. This is the first time I tried it in WinXP though....