As I figured, defaulting the BIOS settings was a bad idea - too bad not doing it during the update screwed something up. After mucking around a bit I looked at the Boot Order and sure enough, the BIOS defaulted to my Maxtor HDD (no OS) rather than the HD Raptor HDD (has OS) because the Maxtor is hooked up to the Primary Slave IDE cable. So I switched the primary hard disk to the WD Raptor, selected it as the secondary boot device (behind one of my disc drives) and presto chango - we have an OS again.

Yeeesh. Okay - back to installing stuff and getting set up again...