I honestly doubt you will be able to run SSE in any satisfactory way on your current PC. It is your graphics card that will be the real problem, not your CPU. The requirement is a 3GHz
singlecore, while you have 2 2GHz cores. It has been hinted to (but not confirmed?) that SSE will support multithreading, meaning that your 2GHz dualcore will, very roughly, equal a 4GHz singlecore in performance.
However, the system linked to by Master Captain has the
same integrated graphics chips as your laptop, and will not offer much of an upgrade unless you install a dedicated graphics card into it (upping the cost considerably). Easily another $200+.
Video card: Geforce 8800GT or ATI Radeon 4850 with 256MB ram (At least Shader model 3.0)
I am very unfamiliar with ATi graphics cards, but from what I can find out, the HD3500/4200 is much, much less capable than the 4850, which is the minimum requirement for an "ok" experience at low detail level.
As has been the general answer in similar threads though, it is a lot cheaper getting a desktop with good specs than a laptop. While there are great gaming "laptops", they are extremely expensive. It will be some time until there will be affordable laptops able to run SSE "without any slow downs" judging from the system requirements.