Just use LILO. Install it to the MBR of your primary hard drive
and it'll allow you to choose the drive and partition to boot off of, be
it Linux or Windows. man lilo for more details on how it's done.
> The large drive would contain a small shared data partition for moving
> stuff between linux and windows.
Why bother with the extra partition? There's read/write support
for FAT32 under Linux. I believe it's in newer kernel releases (late 2.1
kernels and any 2.2 kernel) and might be available as a module for recent
2.0 kernels as well. (Collin knows more about it than I do.)
Matt