By default, (I believe) the computers on the "Inside" get DHCP addresses. You can turn the DHCP server off if you'd like, and just assign some addresses. For two computers, it's not gonna make any difference either way.
If you already have addresses assigned by your ISP, use one on e the 'WAN" side of the router, and do whatever you want with the other one....but, DO NOT use the ISP addresses on the Inside....the router won't work if you do.
Good Luck
Scott