I got my hands on a lenovo T420 4178CAU computer with an intel I7 vPro processor. How good is this computer?

Well, I looked up the specs for it. I'm not sure how good the graphics card in it is. But it looks like an excellent school or work laptop. It has quite a nice processor for a laptop, and the 4GB of RAM is good for school/work purposes.

Depends on what you use it for.