Just try to downgrade to Windows 7 Ultimate SP1, like me

I get 20fps at its worst, 30fps at average & 50fps at its best.
My PC specs are :
CPU - Intel(R) Pentium 4 Dual-Core @2.5GHz ( Only $2 bucks in my country here,

)
RAM - 2GB DDR2 ( $25 bucks )
GPU - ZOTAC NVIDIA GeForce 9500GT 1GB GDDR2/GDDR3 ( around $100+ )
I haven't tried using Windows XP because when i try to install,
I can't downgrade my Windows

even using boot options.
Windows Vista is a bad choice because it limits the Random Access Memory..