That is the maximum for your screen...Isn't it? It isn't a 8600 GT limit. My 1520 has one and I can run at 1680x1050, but that is because that is the max for the lcd it has.
Does he have the same model or just another 15.4" laptop? The 1520 is that size, but you could get it with a 1680x1050 LCD. I think there was also a version of the 1520 that was 1440x900.
Im guessing that 1280x800 is your native resolution on ur monitor, so theres no reason to go above it? I know mine cant get above the 1440x900 native resolution. but if you attach a external monitor that can go higher, then you'll be able to get above 1280x800 on the external monitor, but as for your laptop monitor, i dont think u can go above the native.