you could do try overclocking your cpu your type of cpu should be easily overclocked to 3+, dont know anyting about your cpu but id be very surprised if you could not overclock it with a few tweaks to the bios. dont get to greedy i would not try go over 3,4 without getting a new cooler. its not someting you need to be good at computer to be able to do its just test and try test and try until you find what works.
http://forums.extremeoverclocking.com/showthread.php?t=151373 seemd good OC info when i fast read it
i got the same graphic card as you have and a Q6600 2,4 cpu but i got this overclocked to 3,2 it runs on 1280x1024 on high settings just fine at sim 10-7 for me but this is one of few games that uses quad cores i think.
the classic reinstall your windows or use your backup, ghost if you got one. usually speeds up the comp but oh boy is it time consuming. if your reinstall xp i would advice getting tinyxp (rev9) it reduced my backround programs running when starting up windows and bigger options at installation. (i think its perfectly legal if you got a valid xp key)
http://thepiratebay.org/torrent/4206516/TinyXP_Rev09_-_eXPerience
