Airport Wireless Extreme Base Station - Windows XP Clients Suck

I have spent the last several weeks troubleshooting my wife's computer (Windows XP) 802.11g computer... it has been the most frustrating experience of my technical life. I can't decide if it is her computer or rather the new apple airport extreme base station that I have replaced my Linksys router with. I never had these problems with her computer until we introduced the router and starting changing security encryption levels.