From what you describe, I would think the problem lies within the desktop, and not so much with the router. If the laptop "worked great" in that room, and the desktop doesn't ........well.?
If you still have the laptop, try making a wireless connection in that room again. If it still works great, and your desktop doesn't connect, I would investigate the desktop. It might be the wireless card or it might be the network settings.
I like the wireless extender I got at Radio Shack (not wireless booster, -wireless extender). check it out
