The late 08 MBP or the MacBook? They are different.
As for the trackpad, there is a small screw under the battery usually that will need to be tightened or loosened (if it is not clicking at all). Sounds like a bulging battery to me, if it is bulging it will need replaced (the battery).
Check iFixit.com for repair guides.
I believe the Intel 3000 is only a hair faster, under COD 4, it's able to run it at native resolution all high settings (according to users). In terms of CPU, the i5 is at least 3X more powerful than the Core 2 Duo. GeekBench would give you the exact numbers.