Use:
1. ExFAT for non-Mac bootable but Mac 10.6.5 read/write hard drives that can boot XP SP 2 or higher.
2. FAT32 for non-Mac bootable, but any Mac OS read/writable 4 GB and under drives you can use with any version of Windows to boot Windows.
3. NTFS for non-Mac bootable, but any Mac OS read-only without third party software larger hard drives you can use with any version of Windows to boot Windows.
4. HFS+/GUID to boot Intel Macs, but not boot Windows, and not be readable by PowerPC Macs (pre-2006). Macdrive needed to read from Windows without a network.
5. HFS+/Apple Partition Map /Journaled to boot PowerPC Macs with 10.2.3 or later if the Mac is older than the operating system, but not Windows. Macdrive needed to read from Windows without a network.
6. HFS+/Apple Partition Map/not Journaled to boot any PowerPC Mac with Mac OS 8.1 or later if the Mac is older than the operating system, but not Windows. Macdrive needed to read from Windows without a network.
7. HFS Standard to boot Mac OS 8.0 or earlier Macs. Macdrive needed to read from Windows without a network.
You are only likely to run into 1 through 4 today. Very rarely will 5 - 7 appear.