I need a new HDD for my PC, since my reliable external HDD seems to be having I/O errors lately (

).
Anyway, I found one for US$60 and it's 160GB. It's the lowest price I could find here. I like it. But I need to know if I can actually put it in the CPU.
The HDD I like says it's S-ATA. Ummm, how do I know what mine is? Where do I look, other than inside the case (which I
can't open (please2stoptellingmetodosokthnx))?
Or maybe it doesn't matter? I dunno.
Remember, I'm absolutely clueless about hardware. You'll have to explain it to me as if I were more stupid than usual. 