Trouble Obtaining IP address Linksys router

Hello,

I had to reinstall windows XP home on a dell inspiron laptop for my son. I have updated windows and installed the recent drivers. I have a linksys WRT54GS router. I have an airport express that extends the network and allows me to stream music to my stereo. When I try to connect to the network it will see the network and try to connect but hangs up when obtaining an IP address. The end result is limited or no connectivity. The other computers in the house are fine and the TIVO wirelessly connects no problems. I took the laptop to a coffee shop and was able to get on the network wirelessly no problems. I know I had to change the settings to install the airport express. Any ideas how to get this computer to obtain an IP address and allow it to go online? Thanks!