If you are using DHCP on XP, have you released and renewed your old IP address?
If you ran a ping and tracert on the local XP computer and it returned the old IP#, then check the hosts and lmhosts files located in the folder c:\windows or c:\winnt\system32\drivers\etc\. (Run a search on these files to make sure you've located all the copies.) Next, check TCP/IP settings to see what DNS and/or WINS servers are specified. If XP is configured for DHCP, you will find that your router or another server is providing most (if not all) of the TCP/IP configuration. I don't think the router is the problem. Check to make sure your XP computer is not inadvertently pointing to another computer for DNS or WINS. If you ran a ping and tracert on your Windows 2000 or ME computer and it returned the old IP#, then check the above areas on your Windows 2000 and ME.
Is your XP computer configured with a valid IP address? In other words, do you have a valid registered host name for the XP that is accessible from the Internet?
This was first published in November 2002