Buy a decent cooler for the e7400
set the fsb to 333 [ 1333MHz ] and the chip will almost certainly run well at 3.73GHz
Your motherboard has an intel chipset and cant SLI two nVidia cards .
So IMO replace the card you have with either a Radeon 6870 or a GTX 460 1 gig .. depending on price and on your monitor resolution which you dont mention
if you have a 64 bit OS also consider upgrading the RAM to 4 gig , but if you dont then dont bother