Assuming that you already have both computers and the (non-wireless) DSL router, there is a zero cost solution, if both machines have free ethernet network cards. You connect them by an inverted ethernet cable. The one connected to the DSL modem will be the gateway for the other. Only drawback: the 'main' computer (the internet server) has to be 'on', if you want to have internet connection on the second one.

In case both computers are in the same house (plugged to the same electrical installation) you have an alternative solution to the wireless router, that I personally like very much: internet connection can be redistributed inside the house over power lines (yes, you use your electrical 'normal' plugs). Not very cheap (you need two) but it couldn't be easier: no configurations needed.
I used products from this company: http://www.planet.com.tw/ .

-- José.