There are a few options.
1) Fat32: I wouldn't recommend this one. While both should be able to read/write to it, you will eventually get corruption issues on that drive.
2) Format with a linux fs, and get Paragon. Paragon allows you to have r/w access to ext2, ext3, and reiserFS (IIRC) from Windows. However, it's a pay thing.
3) Captive NTFS Linux driver (or some other Linux NTFS driver): This might be your best bet. I haven't tried it out yet, but it'll allow Linux to read/write to NTFS. There are a couple of drivers out there for this.
I wouldn't recommend using something like Explore2fs - it's slow.
Hope that helps.