Wireless network relay?

"Pretty much anything that can run the excellent DD-WRT can be setup as a wireless bridge (or repeater). But be sure to check the notes, as some of the devices require extra steps!

I've used it on the La Fonera and various D-link, Netgear and Linksys devices. The Buffalo routers also tend to work well, from what I hear. I'd just find a cheap router on newegg and see if it's compatible with DD-WRT and then setup your wireless bridge.

There are also dedicated bridges you can buy, some go by the name of ""game adapters."" But they cost about as much as a DD-WRT capable router (or more) and they're not as versatile.

edit: see SU question: Can I make two wireless routers communicate using the wireless?"

Apples Airport Express is not cheap, but is by far the easiest system I've ever had to configure as a WDS Remote. Having one upstairs and one downstairs solves your problem. In addition, you get Airtunes and wireless USB printing as a bonus.