Desktop connection drops only when card in laptop is active

My wife has a D link DWL 520 card in her desktop running XP SP 2 Home
edition. The connection works great when I am away for work or when my laptop
card is unplugged ( I am running 2000 professional). The minute I plug in my
laptop card and connect to the router her connection will drop within a
minute or two and I will have to repair it only to have it disconnect over
and over. It can't maintain a connection when my card is connected. When the
laptop card is not connected hers will remain connected for days without a
problem.

Any ideas what is causing this ?

Any help would be greatly appreciated.