Ive booted cd's off the C400... make sure the drive is attached before you turn on the machine. Never tried booting memtest, but have booted multiple os's off CD before, the functionality is there. Keep in mind its very early version of El Torito. I have also swapped the cdrom to a HD-DVD drive with no issues. Perhaps thats why mine boots off CD? You can reuse most any slim IDE CDROM/CDRW/DVDRW/HD DVD on it, I can check tomorrow for you what drive I have been using. Upside burns CD's a treat if you got the external CDROM bay, and swap the drive. I think I still have a stock cdrom to test as well. Have a bunch for it, including the dock and the floppy drive.