Here's how:
A few necessities first.
1) An Intel-based iMac.
2) OS X currently installed (don't worry, it will be gone soon enough).
3) Latest firmware updates for your iMac installed. This is absolutely necessary, or even BootCamp won't work. (don't worry, you will NOT be installing Vista via BootCamp,. Never the less, it has to be installed to burn the Windows driver's disk.)
4) NEWEST version of Boot Camp installed (1.4)
5) A full installer disk for Vista (this can be either a "Full OEM (sometimes called a "System Builder Kit") or a "FULL Retail" DVD. Note that UPGRADE disks cannot be used, since to use an upgrade disk, one needs to be able to open the DVD tray after the Microsoft installer begins. This is not possible with Apples, which use slot-loading drives.) Note also that the license associated with the CD key MUST be a valid license. I do not approve of piracy AT ALL.
Now that you've gotten those together, let's start:
First, Start Boot Camp Assistant and do NOTHING but burn a Macintosh Drivers Disk for Windows. Again, DON'T do ANYTHING ELSE!!! at this point. Boot Camp Assistant is ONLY needed for burning a drivers disk in this method.
Once you have this disk burnt, set it aside (don't forget to label it so you won't lose it on your desk somewhere).
Next, put your Vista install DVD in the drive and RESTART your machine, remembering to hold down the Alt key until the Apple Boot Menu appears. At this time, say goodbye to OSX completely, since once Vista is installed, the machine will be an Apple Windows PC ONLY.
DON'T DO THIS if you aren't SURE it's what you want to do. Also remember that if Apple releases any firmware updates for your particular Apple, you will have to reinstall OS X from start, deleting your Vista partition in the process. Using this method, you CAN'T have BOTH OS X AND Vista installed as the primary OS. No way around this. So Make a decision NOW, before you do something to your Apple you really don't want to do.
NOTE that this method requires NO hacks to OS X or Windows, nor does it break either your Apple Warranty, or your Vista EULA. It is completely safe, if you follow my directions carefully.
Choose the Vista Install Disk as your Boot drive from the Apple Boot Menu.
The Vista installer will throw uo a message asking you to press any key to boot from CD/DVD. Press any alpha-nnmeric key immediately.
The Vista installer will begin.
Choose a CLEAN install (that's the only kind you can do at this point). Then choose to do work on the hard drive. Delete ALL partitions on the drive, INCLUDING ALL OS X partitions, as well as the 200MB drive at the beginning of the disk (this is the EFI partition, necessary for OS X to operate). Then create a SINGLE NTFS partition filling the entire drive, and format it.
Then install Vista installation on partition "C:" (disk 0, partition 1).
Once the Vista installation finishes, and you are at the Vista Desktop, remove the Vista Install disk, and replace it with the Windows driver disk you created earlier under OS X. The drivers will be installed.
Then make sure to update Vista using Windows Update. Two very important updates will not be included, so you will have to download them frim Microsoft Downloads. These are:
1) KB