Oh, I see now. Looks like you got a nice deal on it then, I've seen people say they paid $800 in July, I am sure you will be happy with your new Laptop, when the time comes that you feel like you need to upgrade again there will most certainly be better options available.
So does this have the Intel Core 2 Duo Processor P7350(3M Cache, 2.00 GHz, 1066 MHz FSB)? and you wanted to upgrade to a
Intel Core 2 Extreme Processor X9100 (6M Cache, 3.06 GHz, 1066 MHz FSB) for $225.
If the motherboard can support this change which may be hard to find out, unless you already have on the mod videos. There may be a problem with heat as the exteam uses almost twice the power from a max tdp of 25w to a max tdp of 44w on the extream. I would try to use a cooling pad all the time but that is just my opinion, doing so and running on battery power will probably shorten the battery life a bit but I couldnt even guess how much.
Here are some game performance numbers I found that someone posted on your Laptop in stock setup: I get about an average of 40 FPS in WOW, and an average of 30 FPS in BF:BC2. This same person also said that you cannot replace the GPU on this laptop because it is soldered in place.
Here are the links to the two CPU's if you want to compair them, I am guessing you have already:
http://ark.intel.com/Product.aspx?id=36750
http://ark.intel.com/Product.aspx?id=35431