linksys wireless router wrt54g2 setup

LinkSys router signal through wall?

I setup a Linksys Wireless G router (WRT54G2) and my wireless laptop is about 30 feet away and gets an excellent connection right away. My wireless Desktop is only about 6 feet from the Router, but through two walls and either doesn’t find the connection, or if it does, the signal strength is only “Good”.
Do walls affect wireless router signals? I thought that is the whole point of “wireless”?

If the walls are, or have a lot of, metal, they’re blocking the signal. sheet rock and paneling shouldn’t cause a problem at 6 feet = not even 6 feet of sheet rock. There’s something else wrong. Does the desktop have a little USB adapter connected right to the USB jack (rather than being on the end of a short extension cable)? It might be in exactly the wrong position, relative to the orientation of the antenna on the router.

Linksys WRT54G2 Wireless G Broadband Router

router