How important it it to have more power?
Very if you need to upgrade your graphics card. You would need to get the dimensions of your PSU and then try and find a better powered PSU, though I fear this might be difficult.
A couple of cards that should be OK.
A Radeon HD5450 1GB GPU(20w ,35w w/full load).
The Sapphire HD 5570,power consumption is less than 45 watts under full load.