Found a couple of good leads on setting up the Koolu as a MythTV front-end, through persistent searching in specific forums, like the Ubuntu support forums and the MythTV mailing lists. A couple quick clues:
1. Hit DEL on startup to get into the BIOS, use the BIOS options to expand the memory dedicated to the video card. Options are: 32M, 64 M, 128 M. Not sure how much of an effect it will have.
2. Hit Shift-F10 early in the startup (prompt only appears for a second) to disable the RealTek attempt to launch the machine from a network boot image via PXE. This saves 10 or 20 seconds on every boot.
3. The /etc/fstab had an entry for a swap partition, but the UUID was incorrect. Just reassigning the device to hda5 rather than the UUID was enough to get the swap to come up.
4. I’m convinced there’s a way to get a lot more performance from the video, but need to dig in more. The AMD LX800 driver should support buffering, just need to find the trick to turn it on.
5. There’s an error in the Xorg.0.log file that indicates the kernel doesn’t support MTRR and should be recompiled to do that.