...routers are quite expensive...
???

Here is one for 14.99

http://www.tigerdirect.com/applicati...4190&CatId=198

...it connected the the two pcs together, but wouldn't let us connect at the same time...
Sounds like your ISP will only allow you to have 1 IP address at a time. A router will solve this issue.

More Info:

http://computer.howstuffworks.com/home-network8.htm