I'm not sure exactly how my EEE PC got to this point, but I have Backtrack (an Ubuntu-based distro) on the SD card, and a few different Ubuntu LiveUSB distros on different USB memory sticks. If both the SD card and any of the USB sticks are present, the system will present a GRUB boot menu which seems to be the built-in EEE PC one--it has the "reset to factory defaults" option--but all options will boot Backtrack, even after claiming to reset to factory defaults.
If either the USB stick, the SD card, or both are missing, I get a Grub error 21 at boot. Not sure quite how to un-hose this; I'd just like to put a conventional netbook Ubuntu on the built-in SSD, but I can't trivially do that from Backtrack 4.