After I installed the NVIDIA driver on my Slackware12 box, I needed to change the HorizSync & VertRefresh settings in the xorg.conf. I am not at home right now, so I cannot check the exact settings I set. It was something along the lines of:
HorizSync 31.0 - 80.0
VertRefresh 56.0 - 76.0
Modes "1024x768" "1280x1024"
This gives you a rough idea what you are looking for. What I would do is google "1280x1024 HorizSync xorg.conf YourMonitorType". This will give you a better heads up on the exact settings required for your system.