I googled around and found a presentation by Kyle Rankin, author of "Knoppix Hacks", who goes by the nickname 'greenfly'.

OSCON - 2005-08-04
System Rescue with Knoppix
http://www.greenfly.org/talks/knoppi...e-oscon05.html

Read through the presentation and find gpart which is a MBR and partition table recovery tool. The presentation has instructions on how to use gpart.