Backup drive for MAC and PC

I got an external USB drive for backup and file transfer (between my PCs and MAC) only to learn that one does not support the other. 

I tried first formatting to FAT on the MAC, and that almost worked on the PC as some mac files were unrecognizable in windows7.

I then tried formatting to FAT using windows and that's worse. The MAC won't recognize the drive.

Anyone know how to get this drive to work on both PC and MAC?

Thanks

After you format it using Windows, did you re-install the driver on the Mac? I know mine needs to "installed" on every Mac I connect it to.

You say the Mac doesn't "recognize"? You mean it doesn't show up in your peripherals?

I found This which says to use windows, but to do  "Convert to MBR Disk".

I didn't do that. Is that my problem? 

I tried to remember how I set up mine, but it was a while ago and the process was pretty simple actually, so much that I don't remember much. It's formatted NTFS, thanks to Paragon which came bundled w/ the Drive. (Seagate FreeAgent GoFlex).      

I simply installed and formatted it using my MacBook Pro - first thing I did afterwards was to hand it over to a friend who uses PC to transfer files. Worked flawlessly. But we have to run the installer/set up exe file on every new machine we connect it to. 

Did the same in Russia - the computer in the Green Room was a PC, and we used it to dump/exchange files. We brought the External drive, use the little set up app once and we were good to go.

I know this isn't helping - sorry, Tim.

the 2 format parts should work