First. Motherboards in laptops, except in the same range, are not interchangeable. This is because there is no such thing as a standard form factor for laptops. Also, the port layout (USB, VGA/DVI/HDMI, LAN, Memory card, eSATA, etc...) changes between laptop ranges, not just over time. They are all proprietary, each motherboard with it's port layout is designed and matched to a corresponding case and then sold as such.
Second. The max processor for your laptop range is the i7-620M. You'll probably need to get this from the likes of ebay or craigslist as mobile processors are not sold retail. The laptop will need to be broken down so you can access the processor, this can be long, complicated and protracted due to the highly integrated nature of the system, the complexity of the design and to prevent the ordinary user from servicing their laptop. The last hurdle, which I don't myself, is whether your processor is fitted into a socket or is soldered to the motherboard. Obviously, if it's soldered you're snookered.