Networking with 2 LAN card on a PC

I have 2 cards on my PC. One is Onboard LAN card on intel 845 motherboard. And other is inserted in PCI slot. Now I am having shared LAN internet connection 256 KBPS. So I can access net on my PC. Now I want to share to one another PC by utilising second card inserted in my PC. Both PC is having Windows XP professional, p4 2.4 Ghz , i845 MB, 512 MB RAM.

How can I do it ?

Thank you for your answers in advance.