Hi, if you need any clarifications please ask here,
also if you find a solution post back with your results and tips.
The first two lines of my post are part of the welcome message, no offence intended.
I don't have much experience with the 'buntu's, and the names of the system tools may be different to Mandriva.
When you plug-in the old drive, be sure you don't change the order in which the system sees them
as it may lead to confusion when the system looks for the / and /boot directories.
Hope this helps, I'm still learning too ;-)