I think you will find that this has nothing to do with your BB. If you open taskmanager you will find that MSMSGS.EXE is running. This is Windows Messenger (as opposed to MSN messenger). For some obscure reason this starts up completely invisibly and neither I, nor anyone I know, has found the entry that causes this.
The best solution is to try deinstalling Windows messenger in "add/remove programs / windows components".
If this fails then go to c:\programs\messenger and rename msmsgs.exe. This will stop it and should cause you no problems.