After you have clicked ok to confirm your IP settings, open a command prompt and type the following(WinXP machine):
ipconfig /all
Make sure that your DNS server is correct.
Now, type in the following(WinXP Machine):
ipconfig /flushdns
ipconfig /registerdns
Now that you have pointed the WinXP machine to DNS correctly (hopefully) you should be able to get onto that share (as discussed previously).
Post back with your results