Don't know ... I don't have those problems.
I have a core 2 quad 2.4 GHz with 3 GB RAM, a GeForce GTX 260, Vista 32 bit and the game runs fine on maxed-out graphics settings.

My game runs 60fps. Maybe its the drivers or video card? running an ATI x2 2gb 512bit video card. HD4870.

Oh and 4 gigs of ram (because anything higher is ********...unless your unfortunate and got vista.)

I got an
amd phenom quad core 2.3ghz
9800 gtx 512mb
4g ram running
vista 32 bit (unfortunately)

and the game is being outperformed by my laptop which has

duel core intel 2.4 ghz
9600gt m
4g ram
vista also

I can get 60-70 fps in instances on my own.

I get about 30-50 fps in areas with no other people, and few objects.

I get about 20-30 fps in areas with a decent amount of people (like bases). Or when flying in general, with no people around.

I get about 13-20 FPS when flying into an area with lots of people.

Thats with newest drivers, 4 gigs of ram, gtx 260, C2D at 2.6 (or 3.0), x-fi titanium. IMO, with these simple models and sparse objects in the environment, I should be getting more like 60-90 FPS at all times. I could fly into Shatt with hundreds of people around in WoW, back when I had a 8800 gt, and still keep 50-60 fps.