if i buy a 80gb portable hard drive to backup my ps3 will it be fat32? or will i have to do something to make it fat32? please explain how!

depends on the drive . you can use a pc to reformat it if necessary or most can be formatted using the ps3 - just go to system settings , format utility and find it . be careful you don't accidentally format the ps3 instead
you can ask specifically for a fat32 format drive before purchase or just plug into the ps3 to see if it shows up - if you can , first plug into your pc and check it's specs , copy something to it ( like an mp3 file , put it in a folder called MUSIC ) and see if the drive shows on your xmb under the music section
most drives that directly plug into a usb port without an external power supply are now fat32 but ask before buying and make sure they will show you on the package or manual where it says it is , don't just trust the employee