Dude you have to trust me.
The problem is your processor is just too slow, and I willing to bet you have very slow memory.
Take the card back.
I build machines.
I have people asking me the same question over and over..
Why did my frame rates drop?
People think they can go out, buy a new video card, and BOOM!
there fps will increase..
this is so untrue because the newer cards are geared towards newer processors and memory..
I have heard your story a hundred times..
It pisses me off that they do this to people too.
Take not, those frame rates they display on the back of the box.
Read up on what type of computer they did that bench test with.
Go here. and bench test your rig. You can compair your results to people with the same setup as yours.
Then maybe you might believe me.
http://www.madonion.com