If your computers are close to each other or even in adjacent rooms consider networking them with ethernet cards (1 in each) and a cross-over cable connection as the cheapest way of doing this. Although I appreciate the attractions of a wireless network I am still using two pc's in different rooms connected by cable and both share my broadband connection without showing any reduction in bandwidth. What I mean is that each performs as if it is the only connection.
The only drawback for you to consider with my set-up is that my 'internet gateway' machine has to be on for the other to go on line. To get round that I would need a router.