i'd get either, although to let you know the x800 wll use more power and use an external 6 pin pcie power plug. The7600gt does not, the 7600gt is also newer btw...
as prozac said though they both perform similarly, although the x800 doesn't support ShaderModel 3.0, if that matters to you.
your choice, they both perfom much the same, THG did a 'review' (well a review on quite a couple of graphics cards) about thegraphics cards in that price range recently
you cn also chck the interactive GPU charts on the THG homepage.
Your two choices are pretty close in performance. Feature advantage to the 7600GT. If you go ATI, grab the X850XTpe (platinum edition) as it is the same price, clocked higher and a little faster than both the ones you listed.
Oh, No problem. There really isn't a wrong choice. It would be a tough decision for me to go with the slightly faster X850XTpe or the SM3.0 7600GT. It just depends on the game and your preferences. (and how you feel about rebates)
Old review, but it's the first one I found just to give one example of what the extra core/mem clock of the Platinum edition can do for it. Looking at the GPU stressful tests higher res with AA/AF, the platinum edition pulled an extra 4 fps (6%). http://www.guru3d.com/article/content/196/11/