FPS help

I have a serious problem with FPS, I have most of the settings below the Mid range, and I *guess* i have a nice system...but usually only get about 13-15 FPS. :o
Hardy ever do i see it go above 20 FPS
(and thats usually when i'm not around an airport) The only thing in my system that acts slow is FS9, everything else is like a "hot knife through butter"
So I am asking you all, what should I do to get better FPS...I'll even settle for 30 FPS if I can.
My system specs:
Emachines T6520
Windows XP Media center Editon SP2
AMD Athlon 64 Processor 3400+ 2.29 GHz
1.37 GB or RAM
ATI Radeon Express 200 Series (not sure sbout that one, its just what it says on the case
)
Thanks in advance!!
Hardy ever do i see it go above 20 FPS

So I am asking you all, what should I do to get better FPS...I'll even settle for 30 FPS if I can.
My system specs:
Emachines T6520
Windows XP Media center Editon SP2
AMD Athlon 64 Processor 3400+ 2.29 GHz
1.37 GB or RAM
ATI Radeon Express 200 Series (not sure sbout that one, its just what it says on the case

Thanks in advance!!