If it's that first black Intel MacBook, then replacing the HD is SUUUUUPER easy. So I'd suggest you just pop it out and find out the specs from the one that was in there and just go grab something similar.
If you need some instructions (with pictures!
) try
iFixit: The free repair manual. I've had lots of luck there.
As far as brand name, etc. I'd suggest if you just get one of the major brands, doesn't seem like it matters much for casual use.