Since you dont plan on heavy gaming, a fanless 7600GS or x1600 based card should do for you.
If you opt for a beefier 7600GT/7900GS (or the ATI equivalent), you can always invest 25-30$ into a zalman vf700 cooler - they are literally unaudible in their silent mode.
p.s. If you can't find a decently priced passively cooled card, there is software that allows you to modify the fan speeds of most modern video cards (read : the last 2 generations of DX9 cards from either manufacturer). If you're not doing any serious 3d gaming, you can set the fan speed to a low value (30-40% in all modes) which will result in fairly quiet operation. Just dont forget to change that if you plan on gaming at some point.