The 3com bluetooth adapter really sucks. Well, actually the adapter is okay but the drivers suck. 3Com hasn't updated them for a year!! This is the last time I'm buying a 3com product that requires drivers.
For your problem: I was able to force the 3com to work om my XP machine. But it took a lot of installing and uninstalling. I don't remember excactly how I made it work. Your best bet is maybe just to wait until the official support for bluetooth is here for xp.