increase the memory of graphics card.

[Calum]

It's an example, purposely exaggerated.
Seriously though, if you can find a 6600GT, add a replacement cooling system, and then overclock it to match the performance of a newer card costing the same, I would be very surprised.  Whatever you do, that card will not handle modern games.

[JXY]

guess it's time for a new card.

again, check for compatibility. 

[drmsucks]

actually i did want to increase it for gaming.

List the games that you want to play and you can get some specific, suggested hardware improvements for your system.

Best of luck.