AirTunes and AirPort Express, damn near perfect!
I just set up the AirPort Express my birthday gifts bought for me (thanks again Rhonda, Alex, Ruth, Amy, Randy, Mom and Dad!). :-)
Oh man, it's so awesome. It worked right away, it's connected to my USR 802.11g router, and I'm streaming music to it as I write this.
I'm also able to control iTunes from upstairs, even when my PowerBook is downstairs, via Salling Clicker.
The whole setup is so slick, it's sick. It would be 100% perfect if only I could select the AirTunes speakers via my phone. Unfortunately, since selecting "Computer" or "Living Room" via the speaker dropdown isn't scriptable (even in 4.8 it seems), Salling Clicker doesn't have support for that. So, as long as I have iTunes set to use my Living Room speakers, I can start iTunes and select songs and playlists from upstairs.
Still, 99% perfect is infinitely more perfect than the situation was yesterday :-)