Unfortunately i wasn't able to find a chart which had both the 3650 and the 9500gt on it, though this chart did come close..http://www.tomshardware.com/charts/gaming-graphics-charts-q3-2008/Sum-of-FPS-Benchmarks-1280x1024,796.html
When you search through that chart, make sure you look at the 3650 and not the 3650cf, the CF means crossfire (ie, two of them together).
Based on that chart, and based on personal experience (i had a 9500gt) i would say the 9500gt would be the better running card.
Now, that chart is the sum of all FPS based on several games (that way it is evened out and you see less favoritism by the games for ATI or Nvidia). The chart is also based on 1280x1024 because i can only assume that is the resolution you will be running at.
so, 9500gt > 3650
however, a couple things...
You would ideally want to make sure your power supply can handle a newer graphics card. You will also want to make sure you have the correct slot to put the card in, PCI-E or AGP.
Also, from personal experience.. if you have an extra 10-15 dollars, and the PSU can handle it, it is well worth the upgrade from a 9500gt to a 9600gt. When i did the switch, i went from roughly 4000 in 3dMark06 to 8000 in 3dmark06 (with the SM1 and 2 together).
If you decide to get the 9500 don't waste your money on a 1gig version or anything like that, the 512 is plenty.
Hope these help.