I have a similiar computer to yours and I get 30-40 FPS consistantly.
As mentioned, I highly recommend Nhancer to properly set your video
card.(I have the same card as you)

Here is a link to the best information you're going to find.
http://www.simviation.com/cgi-bin/yabb2/YaBB.pl?num=1208959973

Read all of it, but I think you'll know what to skip.  Some of the stuff
is over my head and I was afraid to try it, so I skipped it.

Skip the part where he says you have to do everything exactly as he says.
 BS, I think he's over selling that defrag program.

Skip the O&O Defrag stuff, the windows Defragger works just fine.
Defragging alone will give you a tremendous boost in FPS.

Skip down to Drivers, Nhancer and setting them up.
Start paying attention and reading there, especially
the Nhancer settings.

There are additional links at that website that will show
you how to properly set up Nhancer.
This one is critical: http://www.simforums.com/forums/forum_posts.asp?TID=27540&PID=156769#156769

Use this checklist to install the current driver for your video card.
http://forums.flightsim.com/vbfs/showthread.php?t=160827

Install Nhancer and set it up according to his recommendations.
It will make a tremendous difference.  It did for me.

I hope this helps you.  At least it's a place to start.