Re: Can't install Vista Ultimate but can still WinXP Pro on the same PC. Help!
Some mobo's need drivers to be able to see the drives. I had a MSI mobo that I had to install the hard drive drivers during the initial set-up stage. I think it said something like 'Press F6 to install third party drivers' within the first few seconds on booting from the disk.
Maybe the XP disk has the drivers you need on the disk but Vista doesn't. Did you get any drivers on a floppy with the mobo?