You should check out the new Windows Vista developer center on MSDN: http://msdn.microsoft.com/windowsvista
You can download the bits too!
And thanks to Juval Lowy, if you want to install Windows Vista on a VPC image:
"Might save you some time:
I have a master VPC image of XP-SP2 that I copy every time I install a new build of Whidbey, Indigo or Vista. After downloading the Vista beta 1 ISO file, if you try to use that image directly from the VPC window, it will reject it (DVD, not CD image I presume). You don’t need to burn a DVD – use the WinXP Virtual CD utility to mount on the host OS the ISO file. Then, use the folder icon on the lower left corner of the VPC window to share the virtual CD, and you are all set.
The next hurdle you might face is the type of file system your VPC uses. Vista Beta 1 only installs on NTFS. If you are like me, your VPC disk image is FAT32 (you wanted all the perf you can scrap out of it). So you need to convert the FAT32 image to NTFS. Do so by launching the VPC, and typing the following command in a command window:
convert C: /fs:ntfs
It will complain it cannot convert since this is also the disk the virtual OS is using. Instead, queue it up for the next boot. Reboot the VPC. It will convert the disk once XP has booted.
Now you are ready for installing Vista – from the VPC CD menu select Use Physical Drive, and select the virtual CD you have mounted on the host OS. This will kick start the Vista installation process. It will only allow custom installation (targeting the same drive at the virtual OS). All you need to provide in the machine name. It will do the rest for you."