I have bought at 3Com Blue tooth USB adapter (http://www.3com.com/products/en_US/detail.jsp?tab=features&pathtype=purchase& sku=3CREB96) but i cant get it to work on my PC with Windows XP.
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.