Is it okay for me to ask "if Apples are so great, why is it so many of the people who use them seem to lack knowledge about the most basic of computer configuration tasks? Shouldn't a product so fantastic as a Macintosh help you learn about these things instead of just letting you believe you don't need to know about them?"
Anyway, the easiest way to do this is to buy a NAS drive (Network-Attached Storage) and plug it into your home network. That way people can access it without your computer having to be on.
I have Macdrive installed now and it works flawlessly for me.Downside to using FAT32 on a Mac is that OS X doesn't write to FAT32 volumes very well. It's VERY slow to write to FAT32 when there are multiple files.
How are you looking to share the drive? Will you be hooking it to the PC to share or share while connected to the Mac via a network? As I said, FAT32 performance on the Mac isn't great and there's a 2GB file size limit on FAT32 also. I would install MacDrive on the PC. It allows Windows to mount and read and write HFS+ formatted volumes. It works well from my experience with it some years ago.