Sims 2 laggy

[shafe88]

Why is my sims 2 game laggy on my newer computer. it runs smoothly on my old xp computer and it only has 1 gig of ram and a celeron d 356 paired with an HD 3450.
Computer Spec:
Processor: Athlon 64 x2 4400+ brisbane 2.3 ghz
Ram: 3gigs ddr2
Graphics card: Sapphire hd 6570
OS: Vista SP2

 

[shafe88]

It's laggy like the frame rate is low. I know it's it not the graphics card as it's smooth on my pc with the hd 3450. could it be that the athlon is only 2.3 ghz and the sims only utilizes only one core and not both.