Did your multi-OS setup use to allow you to boot into each individual OS before?
If so, what changed?
What OS did you previously boot into, before you tried FC 7?
The reason I ask is because I too had a multi-OS setup where I had a problem (awhile back) where I booted into XP and I had a problem that required a hard reset.
My problem was that the hard reset or XP (more likely) did something to the partition table that prevented me from booting into anything other than XP.
Unfortunately, I do not recall what I did to fix it (as it happened several years ago).
But it was a simple fix that did not require a re-install of anything!
I take it you tried booting off a linux rescue disc and running fsck?
How about qtparted (??) to see if there is anything funny about the partitions?
Tried "SystemRescueCd" at http://www.sysresccd.org/Main_Page
, it has alot of utilities!