I'd not fix it. Why?
While it is possible to open it up and check the wiring and even replace the pad the fact is it's not your laptop and you could find the machine crumbling inside and losing a friend over this repair. Tell them its a common failure and "get used to using a mouse."
There is a software test I often do. I boot up the UBUNTU LINUX CD. If the pad works there I know someone scotched the Windows OS and the drivers.