I use just such a card in my PC.
Download the drivers and the utility and see if that helps
http://tinyurl.com/2theq
I mainly use windows 2000 as too many things about XP annoy me.
When I did use XP with that card I found I could get better results by
disabling the Wireless Zero Config service (start ->run >services.msc
or control panel applet) provided by XP and just using the Realtek
Utility to handle the connection (rtwlan.exe) .
The Realtek utility handles my connection under Windows 2000 very well
and supports both WEP and WPA-PSK.
The Boingo Client is also quite good at handling connections.