Technically it can be overclocked, but such a weak graphics card wouldn't really benefit and it would get a massive increase in heat. I would recommend a new graphics card if you really need more power.
yes you can. but just don't expect something grand. still remember when i overclocked my 9600GSO. only gain less than 5fps increase but it really helps me to maintain playable frame rates in games
Honestly, I wouldn't even attempt. You aren't going to gain much performance at all, if you really need a performance increase you should look into a new card.