Hefe posted a good suggestion a little back, your router should have a map-ip-to-mac-address function (I know both of mine do). Just set your pc to get an ip via dhcp, then log onto the router and check the list of dhcp clients it has (should only be one, your pc).
note the mac-address, then configure a 'static map' on your router. All that is is telling the router "if a pc with this mac address (enter pc mac addr here) connects then give it this ip"
note the mac-address, then configure a 'static map' on your router. All that is is telling the router "if a pc with this mac address (enter pc mac addr here) connects then give it this ip"