Well the biggest problem when you do a CPU upgrade on a Laptop is heat.
Lenovo and almost all laptop manufactures, design the heatsink so it can dissipate a set amount of heat. Your laptop will be made to cool a 65W Dual core, which is already a hard job for a laptop but adding Another
Two cores and 30 Watts of heat might be pushing it!
What is the Exact model number for the laptop. Im not saying its not possible because it more then likely is, but its a good idea to look into seeing if it will be able to handle it.