Ant writes:

Are you saying my three years old Athlon 64 X2 4600+ 939 CPU would do
fine if I upgrade to an ATI Radeon 4850+ video card?

It's hard to put it any clearer than that. But you can easily see for
yourself, upgrade the video first, take notes. Then upgrade CPU and
see what you got.

I thought there was a bottleneck with my CPU?

Yes?