I had actually given up the idea of running WPA from a live CD, concluding that nobody did it. I went ahead and installed Ubuntu Edgy on my Gateway as a dual boot.
Then I was fooling around with the new Mepis 6.5 release candidate the other day (RC3 now I believe), and popped open the Mepis Network Assistant, plugged in my WPA key and my jaw dropped when it quietly connected to my WAP with no further ado! Apparently the driver for my Intel 3945 chipset was built-in and I didn't have to futz around with wpa_supplicant either!
Not only that but my widescreen 1280x800 display was immediately supported, so my desktop looked 100% better right away. Needless to say, I immediately retired the Ubuntu installation and stuck Mepis on there instead. Ironic that Mepis is based on Ubuntu, but has better details as defaults. I've been very impressed! I've since discovered that I can take the live Mepis CD and run it on my at-work laptop also (which has a troublesome Broadcom wireless chipset). It's not as straightforward because that won't work with the native driver and requires ndiswrapper, but I found that with a short shell script I can connect to the open access point there too, and save that between uses on the Mepis desktop-to-go with a USB stick.
Mepis is cool!