Need help in purchasing new GPU

Raghu Teja

Honorable
May 29, 2013
18
0
10,520
Please suggest the best card for this build.
Intel Core2Quad Q6600 @2.4 GHz
4GB DDR2 RAM @333MHz
Intel DG33FB Motherboard.

The pc will be used for very light gaming, (mostly The Sims 3) and for AutoCAD. I would really appreciate if suggestions are given from both NVIDIA and AMD cards.
Thank You.
Edit: Forgot to mention earlier, but the PSU is Corsair VS450.
 

Raghu Teja

Honorable
May 29, 2013
18
0
10,520


Will it work with the current PSU?
Also, my cousin has an old GTX 550 Ti, used for 4 months. Will that work without any bottlenecks?