After installing the Ubuntu 9.10 beta and trying to start Windows XP from GRUB2, an interesting error message (from Windows) popped up:
Windows could not start because the following file is missing or corrupt:
Please re-install a copy of the above file.
I can assure you that c:\windows\system32\ntoskrnl.exe was definitely neither missing nor corrupt. Fortunately, I had a boot floppy with "legacy GRUB" on it to boot from and had no problem booting into Windows that way.
I tried following recommended procedures, such as using the "os-prober" utility, to try to get GRUB2 to boot into Windows, but all I got was the same error message as above. When I tried booting into Windows from the GRUB2 command line, I got the same error message.
Although I could have installed legacy GRUB on Karmic, I installed Mint 7 instead. I hope Mint keeps legacy GRUB around for a while.