Well I had some worrying few moments last night. My main studying pc orginally just had a 40g ide drive with xp home on it. When I added a Sata drive over a year ago I put vista ultimate on that. My pc has been crashing occasionally recently but I didnt think too much of it, but last night it failed and wouldnt boot. So luckily I found out it was the IDE drive which really doesnt get much use these days apart from games that I used to play on it, so its no great loss.
However my ide drive was the boot and system drive, so all of a sudden I had a perfectly working vista OS but with no where to boot from. which would have been a real pain if I had to reinstall vista again completely just to get the boot loader on there.
But after a bit of thinking I downloaded gparted found here which is a bootable linux distro that is completely designed for partition editing. So luckily I was able to mark the sata primary partition as a boot partition. Then a reboot into the vista dvd and going to the repair options and selecting repair startup problems soon got vista going again.
Before I used gparted the vista disk could not see the vista installation even though it had no problem browsing the entire disk, I am impressed with the repair options you get with vista bar the fact it relies on the bcd to tell it where the installations are.
Anyway situation averted and we have a happy and working pc again!