|1) Ping 127.0.0.1. If you get an OK back your network adapter is probably working OK.|
2. Disable the XP firewall. This is the most common problem with networking XP because it installs with the Firewall enabled and when you install SP2 the Firewall goes back up automatically even if you had disabled it previously. As long as the PC sits behind a router it's protected by the router's firewall so you don't need the XP firewall, really. If you need a software firewall I'd suggest ZoneAlarm or Tiny or Norton Personal Firewall because they're easier to configure and monitor.
3) Once you've worked out the firewall situation ping the server to see if it is reachable. If not you may have to reset the TCP/IP parameters to match those required by your network. Sometimes you have to reinstall TCP/IP to get it working again. XP doesn't make it easy to reset TCP/IP but fortunately there's a NETSH command to roll back TCP/IP to the default settings.
Simply type the following in Command Prompt:
netsh int ip reset c:\resetlog.txt
and any changes to TCP/Ip since installation will be reverted.