I thought it was pretty simple.
Basics:
Boot Camp Assistant is only of use to split one drive for Mac OS X and allow installing Windows. With Windows 7 everything is easier.
For data drive:
If it is going to have a Mac partition (HFS) and something else, erase the drive if you have not, then choose number of partitions (1 or more).
You have to with Disk Utility choose "Ms-DOS" FAT32 and I don't see any reason to use exFAT and because you are just going to format it again in Windows anyway to NTFS.
The drive is empty, and if it had data, you should always have backups, external, and off line anyway at any and all times.
I'd double whatever you think you need; and plan to keep 1/3 to 1/2 free anyway. Maybe 250/750 split.
in Windows and I hope you are familiar with it, just control click "Computer" => Manage and then choose Storage => Disk Management where you will see your drives and partitions.
A. There is nothing to fear
B. Learn by doing
C. Always easier than what this thread has done!
I'm old fashioned, even after a life of 40+ yrs on computers $20-40 for books, manuals, references - that you have handy, able to answer and walk through, still make sense.
Which is why I recommend even long time Mac users to keep a copy (if only to loan out for pesky friends needing help) a copy of "Mac OS X: The Missing Manual, Snow Leopard Edition" 950 pgs from David Pogue. And some pocket reference guides for Windows.