Check that networking is actually running with ifconfig (as root). You should see an eth0 stanza with correct IP info. If that's not there, try running ifup eth0 (also as root) and then checking again.
You're using Ubuntu as the host OS for WMware, yes? I'm pretty sure that VMware is talking to the device driver layer so its independent of any configuration on the host OS. Check the IP info in XP, it should probably be the same as reported by ifconfig in ubuntu, assuming you're getting IP info DHCP from the ISP.
If that doesn't do it you need to reinstall.
just kidding!
If that doesn't do it, check the networking settings control for DNS and hard coded IP addresses for any of the settings and either put in the right stuff, or enable DHCP.
Good luck, I can boot into ubuntu and look up more stuff later if you need.