Good evening -
As a follow up to my prior post - I was hoping to get some additional information regarding attaching an External Drive to my Airport Extreme and getting it to be accessible by both a mac and PC.
I have attached a G-Drive Mobile formatted for Mac to my Extreme Airport; when I do this I can see and access it via my Mac but I cannot see it on my PC.
Does anyone know why this might be? Do I need to partition and format the drive for both or is it something simpler than this?

Thank you for your help.

The hard drive does not need to be changed, unless it is NTFS format.
All you need to do is connect and mount the drive, on either your Mac, or a Windows PC connecting to the same network.
http://support.apple.com/kb/HT1331
more
http://support.apple.com/kb/HT2426
Also, refer to the user guide for your Airport Extreme
http://manuals.info.apple.com/en_US/airport_extreme_5th_gen_setup.pdf