Hi
I don't know if you have already had any success with this but I had the same problem but did not find any info on the net.
However I did find out why it did not work originally and found the cure.
This may work on other PCs as the problem is with the BIOS settings.
I have got Windows Vista dual booting with Kubuntu and it works without any problem.
Switch the PC on and press the delete key to enter the bios settings
There is a setting for the operating system and the default is Windows.
Set it to "Other" not "windows & other" as this probably won't work either.
After this is done you will be able to load any distro you want.

Smeghead