IMHO, stay away from the LinkSys WUSB54G, I've had nothing but disappointing performance, and system instability, because of it. (Actually, I have it paired with a LinkSys WRT54Gv2 too, so I suppose either one could really be the problem. Quality and stability on both units leaves a bit to be desired.)
My biggest problem, is for some reason, the client NIC starts to ping-pong between 54Mbit/s and 24Mbit/s speeds, and while that is happening, no data can pass. Signal strength and link quality, as shown by the LinkSys wireless client util, are both fully-green bars, so signal quality/strength should not be a problem at all. The two devices are in two rooms a hallway apart from each other. Interestingly enough, I've spent the last many hours downloading from Usenet, and no problem. But when I wanted to watch a streaming newscast from a local station about the Red Sox game, it kept cutting out. I could pull up the network properties for the connection, and you could watch, side-by-side - when it started to change speeds is when the streaming would halt. Yet the player would still show "playing". Very frustrating.
The problem was worse before, when I had the WRT54Gv2 set to "G-only" mode, believing that it would be faster, since I only have a single 'G' client connected to it as well, but after a few days, my internet connection, web pages, everything, would grind to a halt. A reboot of the router fixed it. Since I set the router to accepting "mixed-mode" clients, the problem seems much reduced.