How do you format a portable hard drive to use as a giant flash drive for very large files for Mac and PC?

Hi,

As in the question, I have purchased a WD My Passport Ultra portable hard drive because I need to back up and transfer extremely large files (minimum 20GB) between Mac and PC. I don't want to back up the whole system, I just want to put files in it like a flash drive.

Does anyone know how to do this?

I have found instructions for using hard drives as flash drives and for making them compatible with both Mac and PC using some sort of Fat32 formatting. However, I understand that this is no good for large files and so would be no good for me.

Please help!

Many thanks,

Emma