If you go to AMD you have to buy a new motherboard, where's the savings in that?
9600gt is a large upgrade from a 9500gt. The 9600 has 3 times the memory bandwidth as the 9500.
Your motherboard supports the latest quad core CPU's, so you could take the money you save on buying an AMD motherboard and CPU and just buy a better intel CPU. Honestly the E7500 is just as good as the Phenom II 545 dual core, it's a good bit better than the athlon II 240.
The E7500 is a decent gaming CPU. It's not your bottleneck at all. What power supply do you have? You first need a good power supply, then you can upgrade your graphics card. After that you need to pick up a dual channel kit of 4gb of DDR2-800 ram (2x2gb), Then you will have no more bottlenecks, and a great gaming PC.
You can always overclock your E7500 for better performance if needed, but you shouldn't really need to if you get a decent graphics card.
Whats your max budget for a graphics card if you kept your current setup? But I need to know what power supply you have first.
Shameless plug- If you are really into going AMD, I have a setup right now that would save you some $ for sure-
http://www.computerforum.com/163944-am2-mobo-athlon-ii-245-2gb-ram.html
Hell I even have an MSI 9600gt_1gb if you are interested for $60 more. If you sell your intel stuff you'll probably atleast break even if not make money on the deal.