I might be wrong, but your mac will read a FAT32 partition, while your windows won't read the mac partition. What you can do is save all the stuff you want to go between OSes on a FAT32 drive, be it your windows partition or an external HD.
The problem, though, is if you formatted your Windows partition as NTFS, then you're screwed if you don't have an external HD. I think.
Though NTFS is more stable, supposedly, anything I might ever connect to both Mac and PC I make FAT32, just in case.