Code:
[DSL MODEM]
|- [HUB/SWITCH]
|- [LINKSYS ROUTER #1] -> PC 1
|- [LINKSYS ROUTER #2] -> PC 2
You have to have a separate modem that doesn't have an integrated router. The linksys router doesn't support two WAN IP's, only one. In the configuration above, the only good the router actually does is give you a firewall. If you didn't care about that, you could plug both PC's straght into the HUB/SWITCH and give each a static IP configuration with one of the two IP's.
.. but you won't make it work with only a single linksys router. It's a cheap home-office, single-IP router not designed to do what you want it to.