Q: My system : win XP AMD Athlon 64x2 Dual Core Pro 6400+3.21 GHz. 3.00GB of Ram 2x 7950 Gt Nvidia SLI
A: your system is 3 years old. if you are using it to play games then dont install vista. vista will work fine with 4ghz but because its a little old machine not as fast as xp. i recommend buying a new pc or installing vista only if you are not using programs like 3d studio mark, photoshop etc or you are not playing games