What do I need to make my 100BaseT router ALSO wireless?

We just bought a new router and most of our computers are set up to use it and I don't want to replace it or spend a lot of money, but my brother just got a laptop with 802.11b wireless network built in. How can I hook him upto out network the cheapest? Is there a cat5->wireless adapter I can buy or even a USB thing that would let his computer and mine talk? Thanks!

edit: Saw another post. Perhaps an image would help visualisation.

Oh yeah. Another thing that I just remembered is that in a few days I'm going to be using that port for another wired computer. Is there something I could use that just plugs into a computer since the new added comptuer will have two cat5 ports? I could also use USB too...

cheapest I've ever bought a wireless router AR was about 10 bucks.

It would be cheaper and easier just to buy another wireless router.

Although, an alternative is buying a wireless NIC for one of your normal PCs, and using Ad-Hoc (wireless NIC to NIC), and Internet connection sharing, but then you have no access to shared folders except the PC with the wireless NIC. The wireless PC would need to be on when you want to use the Laptop for internet.

if that's my only soloution, he's going to be stuck on dial-up for a while. It's a much older machine and it runs windows 95, so configuring it might be a bit tricky. It's not even his yet, but he believes that the place that's letting him borrow it forgot that he has it. It's not really much of a machine anyway. They keys are about 1/2 as big too. pain to type on.

Another option could be plugging it in with an ethernet cable. Although all of your ports are full, it would generally be alot cheaper to get a cable and a switch than to get a good wireless router. You might be able to find a cheap wireless router around, but idk.