Re: Can't install Vista Ultimate but can still WinXP Pro on the same PC. Help!
The Intel website has a boot disk maker for the P35's SATA chipset if AHCI SATA is enabled in the BIOS. I haven't installed Vista on my P35 yet, but I did this with XP to be able to turn on this support.
Once you make the floppy disk (maybe make it on another PC and copy flash drive) you should be able to press F6 and install during the first stage of the Vista install.
The file is called f6flpy32.exe or .zip something like that.