This is a kind of "cheat" to fix dual boot probs, but how about using a third-party boot loader?
The best I've used is boot magic (comes with partition magic), but there are a number of free ones that work fairly well. The best free one I've used is
XOSL.
These generally work by detecting the boot files in the root partition of the OS, and loading them from there. So the need to have the NT bootloader updated and correct in the MBR is avoided - these do it for you!
Hope this helps someone.
Cheers
Mick