|Presume you are connecting from a broadband or other modem into one of the LAN ports of your PC. You then connect by crossover cable from the second LAN port to the second PC.|
There is a walkthrough in XP Help & Support menu that will show you how to set up ICS ( Internet Connection Sharing ) . No need for us to re-invent the wheel here when the info you need is already in your PC.
Goin' Fishin' (Some day)