HOW TO: Install Vista Beta 2 on a MacBook Pro
After a few false starts I have finally got a working Vista up and running on my MBP. This is 
assuming you already have a working copy of XP installed using BootCamp. Here is what I did:
1. Download the .iso and burn with Disk Utility. I got errors during the install using the disk I burnt at 4X so I tried again at 2X and everything worked fine. YMMV. Make sure you have a Macintosh Drivers for Windows CD handy (you should have made one when you first installed BootCamp). If you don’t, Navigate to BootCamp Assistant.app and Right Click>Show Pakage Contents>Contents>Resources> and mount Disk Image.dmg, then copy the "Install Macintosh Drivers for Windows XP.exe" to a CD-R or what have you.
2. Write down your Product Key. Nothing like waiting for the Vista installer to startup and then realize you have to quit, boot back into OS X and write it down and start all over again. HOWTO: Vista on a MacBook Pro - Mac Forums