External HD Truble

To be accessible from a Windows PC, an external drive needs to be partitioned with +partition map scheme+ of *Master Boot Record* and volume formatted as FAT32 (called "MS-DOS (FAT)" in Disk Utility). This is true, even if the "Windows PC" is a Mac running Windows XP using Boot Camp.

If you want a more seamless experience running Windows on a Mac, you may want to consider using VMware Fusion or Parallels Desktop. There is also a free (but less well-developed) program from Sun called VirtualBox. These create virtual hard drive disk images, and you can store those image files anywhere you want, so you don't have to have a partition formatted for Windows. You are also running Windows under Mac OS X, so you can run both Mac OS X and Windows programs concurrently. The downside is performance, if you intend to run motion-graphics-oriented apps and games; you don't get the same low-level access to the graphics hardware compared to booting Windows directly using Boot Camp.

Hi superfly900

I can tell that your rethinking your backup strategy, I've done it myself time and time again. 😉

Time Machine can not use a windows formatted drive and windows can only write to a Mac formatted drive with additional software like macfuse.
http://code.google.com/p/macfuse/

Ideally your Time Machine backup drive should only be used for that, with perhaps a second smaller partition setup as a bootable clone. One problem that might crop up down the road, is that 320GB sounds a little small and if you have to resize your Time Machine partition the second partition will be erased.

It's hard for anyone to suggest exactly what best suits your current or future needs, but it really sounds like you need a second external HD formatted MS-DOS FAT-32 to use for windows backup, storing and sharing file's to and from both your OS X and Windows.
http://www.macworld.com/article/51972/2006/07/ww_drives.html

Example:
I have two Maxtor FireWire drives setup *"GUID Partition Table / Mac OS Extended (Journaled)"* one for Time Machine and the second has two partitions, both bootable clones 10.5.8 and 10.6.1..

I also have a WD Passport setup *"MS-DOS / FAT-32"* nearly full of photo's and music so that I can share them with friends and family that have windows systems.

Dennis