Upgrading a laptop with an Intel Core i7

[Cola]

First of all, the CPU socket of your motherboard is a PGA, meaning the CPU can be replaced. If it was a BGA type socket, your CPU would've been soldered on, meaning you would not be able to remove it as you would with a normal CPU.

Next off is BIOS compatibility. A T9900 will natively run up to a T9900, but this would only be a 10-15% gain over the T9400. I haven't really looked into the T500 at all, but Thinkpads have a very large fanbase compared to other brands, so have a look at this forum and see if you can find some more info on it, perhaps make a thread in the dedicated T500/T510/T520 subforum
http://forum.thinkpads.com/index.php

The people in there, are very dedicated to the Thinkpads, so some of them should be able to help you along on your project