Not sure that statement is actually true.
I will believe that your PC or Mac has Bluetooth capabilities but the connection to the TimeMachine would not be BT but plain old 802.11g/n wireless.
While we're on the subject, are you sure that TimeMachine is the correct name for your device?
Are you sure it is not a Time Capsule?
If the Mac does not drop its connection to this device, I would look toward the XP box for the solution.
I posted a similar question on a Win forum but not sure it is a win problem. I have an XP laptop with a wireless connection that seems to drop and reconnect constantly to my TimeMachine airport. I thought it was the firewall on the laptop, but that doesn't seem to be the issue... How do I tell if the Airport itself is causing the problem?? My desktop is bluetooth not airport...
AFAIK all airport software is up to date and I'm on 10.6.3 OSX