Sharing the ISDN line

i have a 64Kbps ISDN dial up Line, i dial to my ISP from my NT server. i want all the other systems to use this NT server as gateway to which the ISDN line is connected.
i get a different IP address from my ISP each time i dial my ISP.

How do imake this NT server to act as a gateway to all other system & share the 64Kbps line ??