Automatic IP addressing (also known as DHCP) is never a problem on a network where everything is setup correctly. If you are sharing FROM the XP machine, make sure your TiBook is set to automatically receive an IP address, or Windows Internet Connection Sharing may give you some problems. That's probably true the other way around, but I've never messed with static IPs while sharing from a Mac...
One of the great things introduced with the Snow ABS was the second, LAN-side, ethernet port, which has been retained with the AEBS. Go ahead and use it, and see if your problem is network in general or wireless specifically.