Just ask the person working there if you can install it into a laptop or something, if it's compatible with a laptop, it's compatible with a PS3

My friend recently bought a 1TB external HDD... He intended to open it up and use the inner part (the actual HDD) for his laptop, it turned out that it was a different format and wasn't compatible

And @the bolded, if you don't care about your old data, you can just take out the inner part of an external HDD and put it in your PS3
If you want the old data (saves...etc), just back it up before you replace the HDD

ok thanks that means i'm not stuck with flashdrives?

What do you mean? - - - You transfer your data to flashdrives when your HDD is full? I guess not then