So, it took a little fighting, but I got my Airport Express to join my Linksys WRT54G home network as a client. Now, granted, this *could* have been much easier than it really was. I use MAC address filtering on my Linksys, so the first thing I did was add the AX's MAC address into my allowed list. I then went back into the Admin utility and set up the AX to be a client of the Linksys. I promptly then lost all communication with the AX.
"Hmmmmm" I thought.
I reset the AX again, go through the steps...no dice....
"D'oh!" I thought.
Reset it again, set it as a static client....nope.
Open up the Linksys and, wait, my MAC address is gone! So I have my roommate get me the MAC address again, I type it in, still no dice.
At this point, I'm really craving an AirPort Extreme, but I decide to disconnect my AX and plug it directly into the Linksys unit to set it up, when I realize my buddy, who works in IT, had me enter in the *wired* MAC address, not the *wireless*....
Slap that MAC address into my allowed list and it's worked great since. It is still running as a static IP, though that doesn't worry me too much, as it's much higher in my lease range than any amount of computers in my home will touch. I've been too weary of doing this again to try switching back to DHCP, but I hope someone out there can learn from my exprience.
No regrets so far though. Sound quality is very good. Except for when you have family in town staying on your sofa bed and you accidently start blasting music into your living room instead of on your local computer speakers. (yes, I did do that!)