Get a router and you won't need 2 IP's. Unless you need 2 for some reason. You can pick up a router pretty cheap and share files on the 2 comps etc. for less than 2 IP's would cost for a year.
i got a router (linksys wireless-g/speedbooster model# WRT54GS), it is sharing 2 computers, ps2, and xbox. and i like to play ps2 and xbox ALOT. and if i am playing ps2 online. other peeps want to play xbox online and that would LAG alot which i do hate and also slows down computer