Using 2 NICs to route across two LANS

Hi,

I have an ADSL modem (router) with a fixed IP address of 192.168.254.254 which I need to access from PCs on my LAN IP range 192.168.1.0.

I have put 2 NICs into one PC one NIC has the IP 192.168.1.105 and one has IP 192.168.254.253.

I can access the router from this PC.

I believe that there is a way to make WIN98se route my LAN onto the ADSL Modem using the two network cards but cannot make it happen. Could someone give me step by step instructions please