I did not want to bore you with any info that may not be relevent, but since you are so helpful this is the layout on my PC. I have 3 hard drives.
My first Hard Disk is partitioned into C:/ and D:/. The C:/ is 20GB and has XP installed on it as well as Installed Programs there is 9GB of free space left. My D:/ is 54GB and has various files, leaving 20GB of free space.
My 2nd Drive is partitioned into 2 partitions The first is E:/ and has 17GB free space and the second is F:/ which has 13GB of free space. My 3rd Drive is G:/ and has 70GB of free space.

I am not too sure when you say "As long as you make that dd backup of the mbr" as to what is involved.