May as well post again instead of editing my post out of existance.
I just looked up you model and it's very possible that your gpu (as well as cpu) are causing the performance, as generally the more recent the os the more graphically demanding it is. For that gpu, I suspect windows 8 might be a bit much.
That's all unimportant though as you probably can't upgrade the gpu, and even if you could, you would just make the cpu bottleneck more obvious.
The best solution would be to just buy a new laptop as money spent on this one would not improve it enough to make a noticeable difference.