If you want the "Data" partition to be accessible by both OS's, you'll need to format it as FAT32/MS-DOS (unless you want to use third-party solutions). If you don't need it to be accessible to both, I recommend you just absorb it into the system partition. I'm pretty sure that Bootcamp just gives you one partition, so if you want 3 partitions with one being NTFS, install OS X and bootcamp, cut a chunk from the OS X partition with a re-partition (new in Leopard), and reformat it to NTFS in Windows.
As for renaming drive letters;
http://support.microsoft.com/kb/307844
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Power to Burn.
At speeds of up to 733MHz,
The most powerful Mac in history
burns CDs, burns DVDs, and
burns Pentiums
- apple website, oct 4, 1999. advertisement for the powermac g4