Here's my recommended Setup:
Partition your hard drive into 3 partitions while booted into Leopard.
1) You Mac OS X partition, formatted to NFS (already done)
2) A 'Windows' partition, formatted into MS-FAT32. Now, Windows Vista requires NTFS+. When installing Vista, select this partition and format it to NTFS+. It is important that you FIRST format to MS-FAT32 in Mac OS X, or else the install won't be able to re-format. Since Vista requires NTFS+, and Mac OS X can only READ NTFS+, this presents a small issue if you ever want to file share between the two OSs, hence.............
3) Create a third partition as a swap drive, formatted to MS-FAT32.
Now install onto Partition 2 and your good to go. On each System, you'll see a SWAP drive and a system drive.