No, you can't mess with laptops. Buy a new pc
Umm, false. OP, it depends on what dual core you are talking about for your particular laptop. I notice that there are G7' that use AMD and some that use Intel.
Dude, first off the mobo will be incompatible, secondly, having a better cpu won't really make a difference if all the other components are out of date too.
We don't know if it will be incompatible till we find out what CPU exactly they have. I have upgraded a CPU in a laptop before, and my current one is upgradeable as well. My i5 sandy bridge laptop will hopefully be seeing an i7 upgrade soon, as it was an option for my laptop. If his laptop is a sandy bridge Intel, as some G7 series were, the upgrade is still worth it if they have a pentium or celeron that is also Sandy Bridge.