Assigning NIC card to Internet

Hi,
I am using wk2 adv. server with two NIC card.One is used for private network and second i want to use it for internet.I am using dialup connection.I want this thing internet comes to second NIC card and second NIC card pass it to first NIC cardso that my users can share internet.I don’t want to use ICS and any third party software.How i do it.
Is there any step by step guide pls mention it.
Anurag.