1. Installed GeForce MX 400 card. I originally intended this to be for secondary display, with onboard for primary. Turns out it works much better to use the GeForce card by itself... primary on the VGA connector, secondary on the composite connector. Using the Video Overlay options, setting "Full Screen Device" to Automatic displays the video in full screen on the secondary monitor (even if its not full screen on the primary)
2. Installed RoadRunner. After many false starts, got it working pretty smoothly. Turning ON the dualmon setting worked perfectly (after setting the above full screen video option in the nVidia drivers). It's coming together!
3. Plugged the computer (still running on a regular AC/DC PSU at this point) into a KillAWatt monitor and so far, at peak load (100% pegged CPU, playing DVD disc, crazy hard-drive access) I'm only drawing 113 watts. I still have a couple USB devices to plug in (GPS, wireless network, and maybe radio tuner). I'll check again once I've got them plugged in.
Next up, build the case...