In Windows XP I used the Virtual CD-ROM Control Panel Utility from Microsoft to mount ISO images to virtual drive letters, but surely Microsoft has built this functionality into Windows Vista, right? Wrong. It would be nice, but they haven't built this into the OS yet. I hope they do in the next release. Well, this utility doesn't work under Windows Vista. I thought I was out of luck, but a quick search revealed a new option to try.
The new utility I found to mount ISO images under Windows Vista x64 is the Freeware MagicDisc from MagicISO. This utility runs as an icon in the taskbar and allows you to easily mount/unmount ISO images from virtual drive letters. This utility in fact allows you to mount up to 15 ISO images to virtual drive letters simultaneously.
This is a pretty neat utility, I encourage anyone using Vista to go check it out. They have two seperate downloads for "Windows 9x/Me/2000/XP/2003/Vista" and "Windows XP/2003/Vista x64 Edition"; so it should work if you're running either 32-bit or 64-bit editions of Windows, just pick the right download.