I once followed a trick on MacOSXHints.com to partition external hard disk into two: (1) HFS+ for Mac and (2) FAT32 for Windows. Although the hint worked well, eventually it became a hassle to manage two volumes. Windows computer needed to access data off of HFS+ volume from time-to-time and frankly, FAT32 isn't very efficient nor robust.
So I bought MacDrive for Windows, which is great for reading and writing HFS+ volume. It was well worth it.