Why not get an internal 1TB hard drive? I bought one, just haven't installed it yet.
I tried putting my 500GB laptop hard drive in my PS3, no bueno.
Looked it up and apparently not all laptop HD's will work due to the read/write speed.
Trying to download anything on it, would cause it to freeze up after about 5 minutes or so. I remember when I preordered Madden digitally, and the DL kept getting stuck at like 19%, took me an hour to realize it was the HD and put back in the stock one.