my pc and the fps proplem (((help)))

i have proplem with fps in my game its 8 or 12 or bad than or som time 19

my pc motherboard GiGABYTE G41MT-S2PT
RAM 2G
cpu or pross is 3.00GHz cash 2m
Video Card 1G
hard 160 data
c:free 12G
i use WINDOWS naw sp2 and when i use sp3 or 7 i found sam fps


plz help what i do to get good fps