did you reinstall your OS when you put the new cpu in? Im not 100% sure of it on vista, but i dont think xp will detect a second core if you drop it in without reinstalling. like i said, i dunno if vista will or not.
You don't need to re-install the OS to go from a single to a dual-core processor, in XP or Vista either one. Either will detect the dual core CPU when you drop it in. The CPU you upgraded to is the exact same speed as the one you replaced. You won't see any frame rate increase's. You should however expect to see "smoother" frame rates without as big of dips and peaks. The second processor core, if it is correctly installed will handle background tasks better, leaving more processor power to run the game. Check to make sure you have 2 cpu charts in your task manager. Run the AMD dual core patch.
@jitpublisher: the system may detect the dual-core CPU. Trouble is, the 'driver' to load here isn't a simple driver, it's the whole NT kernel compiled for Symmetric Multi Processing (SMP)! Check that in the Device manager, 'Computer' is set on 'SMP Multiprocessor' or 'ACPI SMP' or something. Switch to one you think is good, and reboot.
With Vista you don't need the dual core optimizer. It's built into it. Ignore the Vista performance score. It's useless. You should make sure your motherboard has the most recent bios. Also, what brand power supply do you have? How many 12V+ amps does it supply? It may not be able to handle the more power required. Run CPU-Z and see what it says. Run other benchmarks and get the results. We need more info to help you. Also that's two graphs side by side in that screen shot, so it sees both cores.