PS2 Slim controller

the PS2 has USB ports and i wanted to know can i use a computer game pad on it? if i tried would it fry my PS2 or my gamepad? if not what are the USB ports for?
http://img134.imageshack.us/img134/7806/ps2yg4.jpg
also i wanted to know whats different in the slim and full size version of the PS2?i know in the small one you can't put in a hdd but is that it?
http://img170.imageshack.us/img170/6132/ps22qi9.jpg

 

bump. someone has got to know.

 

Umm well probably nothing would happen, the PS2 won't recognize an unknown USB controller so it's basically like plugging in a piece of metal with a cord and some plastic attached. Other than that the USB ports are for Headsets and Keyboards and sometimes a mouse.