Low Fps !

Hello Everybody !
i had a question because i can´t play with 25-35fps anymore on full server it´s annoying me allways that low Fps .. My Graphic card is : "Geforce gts 250 (1gb) " and my Processor .. bad i know :S "Amd Sempron 1.61ghz" and i think i got low fps because of my Processor so i wanted to ask if I buy a better one ... Dual Core 3.2Ghz x2 ... Will i get more fps .. what do you think about that?.
My Ping is Ok 35-40 thats not the problem.
Thanks!