Click on Start > Goto 'run' and enter 'msconfig' then press OK
click on the 'Startup' tab, which is the one furthest to the right or just before 'Tools' then select 'disable all' then press OK. The system will now ask you to reboot etc. reboot the computer; this should disable any third party wireless software after rebooting.

Click on Start > Goto 'run' and enter 'services.msc' then press OK

In the Services (local) double click the 'Wireless Zero Configuration'

Make sure the Startup Type is set to 'Automatic' and the Servic Status is 'Started'

Close down 'Services'.

Go to the Network Connections window and right click the Wireless connection and select properties; you should have an tab marked 'Wireless Networks'; select this tab and check the box 'Use Windows to configure my wireless network' then delete any entries in the 'Preferred Networks' if there are any then press OK. This should ensure XP is managing the wireless connection.

Then right click the wireless network icon again and select 'View available Wireless Networks'; hopefully you should see your network, if you don't then the Wireless adapter may have some advanced settings such which may need to be changed such as the wireless mode;

Again right click the wireless network icon and select 'properties', click on 'configure' then select 'Advanced settings'; here you will find a list of parameters; it may be that the wireless adapter might be set to 802.11A/N/B/G or a combination of these letters, you'll need to find the parameter to set the wireless adapter to just 802.11G or 802.11B (depending on the routers wireless access point capability), then save the advanced settings.

Then try again to find you wireless network etc. i.e Windows should prompt you for your WEP key or WPA passphrase if the router is secured.

If your wireless connection then connects but aren't getting an IP then make sure that your TCP/IP properties are set to DHCP i,e. obtain and IP and DNS server automatically.

If all else fails you may need to check that the router doesn't have a MAC address table enabled to only allow certain wireless adapters with specific MAC addresses to connect. Some folks will use this as a security measure even if the wireless security is disabled.

Still not working - take it back and get another one.