My friend has a 2008 MBP 17in, running Leopard. She is having random freezes, especially viewing,using PDF files. She ran Apple Hardware test, and the following came up-4YDC/1/4000003: Video Controller.
I do know that she has never restored her system software, but does have all updates to leopard.
I suggested to wipe and install Snow leopard, but if the video card is going out, that won't work.