The first trick is to find out what it wants a driver for. If the machine originally came with win7, Lenovo's tech support page may have a tool that will do this for you.
Otherwise, open up the device manager and find the bad device (probably a white exclamation point on a yellow triangle). Open the properties of that device and find the vendor and device strings (sorry; I can't post pics right now). Saga Lout gave great directions here:
http://www.tomshardware.com/forum/274306-45-video-controller-compatible-driver-windows-free-download , including the site that will decode them for you. Good luck.