With Windows 7 you'll want (almost need) more then 2Gb of RAM to run decently, especially since the rest of your system is on the lower end of the spectrum. Try with the Detailed Terrain off and Bump Map on and 512 Textures (assuming you are running higher), or even 256 Textures (I don't know the 4350 except that it is low end). Keep Shadows off.
Also, "The only thing running in the background while I play is trackIR."...you wish. I don't mean that to sound mean, but Windows 7 comes with a lot of running processes, and unless you've trimmed them down it's doubtful your computer can keep up with all those and AH. My Windows 7 has about 40 running when I am idle (and uses close to half my RAM due to it), but there are more I could close to gain a small step in performance, but I don't need it since I have a good system, that is something to look at, see how far you can trim it down.