Ok, well Vista will only accept the config it is on as a primary partition so what you will need to do is:
1. Set C: is primary
2.First: install WinXP on D:
3.Then install Boot Magic software and use this sofware to install Windows Vista on C:
I dual booted mine just fine. I had xp pro on the first partition. Used partition magic to create the second partition. Booted off of my install dvd. Ran the installation. And everything works fine. When I start the computer I get a boot menu asking which version to load.