|Insert Mac OS X Install Disc (this part should work with OS X 10.4 Tiger or OS X 10.5 Leopard discs).|
Reboot. Hold down C key during reboot Do not start the install.
From the Utilities menu, select Disk Utility. Select your hard drive from the list and then click the Partition tab / button. Click the Options button and select “Master Boot Record” as the partition scheme.
From the Volume Scheme drop down list, select 1 Partition. Select MS-DOS (FAT) for the format (not that this matters since you will reformat it using NTFS during the Vista install).
Reboot. Hold down the Alt/Option key turning reboot.
When the graphical boot menu appears, hit the eject button. Take out the OS X Install Disc and put in your Vista with SP1 install disc.
Proceed through the Vista install.
When you come to screen titled “Where do you want to install Windows,” select Disk 0.
There will be a message saying that you cannot install to that disk because it is not formatted using NTFS.
Click the Drive Options link. Click the Format link. Click OK in the confirmation dialog.
Now select Disk 0 and click Next.
The Vista installation should proceed as normal.
Once Windows is installed and loaded, insert an OS X 10.5 Leopard disc and install the Windows drivers from Apple.
Thanks to "Derek Hatchard's Information Flume Ride".