I have a 2.4ghz Intel Core 2 Duo with 4GB RAM with the Nvidia 8600GT graphics, there is absolutely nothing wrong with these graphics chips, please who are advising against them have probably never used one or are scaremongering..... Mine failed way back, apple replaced the logic board (after blaming me!!! I had a big row with the "Genius")....
Anyway, now it's done it's been running games and such for about 2 years without problem, I'm sure if they have been replaced, the issue has been resolved and you will be good.
Unfortunately you are wrong, that is why NVIDIA, put aside literally 100`s of millions to deal with this very issue. The premature failure of the GPU`s was extensive affecting many notebook manufacturers. Some will get lucky, my own Early 2008 MBP is still on it`s original Logic Board, some not so; going through several boards, some lucked out with Apple`s great customer service, getting a completely new replacement MBP.
One of my corporate Dell Notebook`s suffered the same fate and the motherboard was replaced three times, each time for NVIDA GPU failure. There is no fix, the 8600GT GPU`s are prone to premature failure what exact percentage only NVIDIA knows and they are not exactly wanting to spill the beans.
Point being for someone on a tight budget this is an increased risk, especially as these machines are starting to go beyond Apples agreement of four years. Apple will only honour the agreement is the machine boots and can be tested, if not it`s on your $$$ a machine this old is just not worth such an expensive repair, and in the OP`s case it would put him straight back to a NetBook....