I have a HP 8400 with a Nvidia NVS 285 video card. It has a DVI splitter attached to it and branching to the Dell 1800 FP monitor and a Epson Projector.

Monitor works fine, but the projector does not display, it only displays multicolored lines.

What do I need to do to get both to display at a 1280x1024 resolution?

By "splitter" I assume that you mean a connector that plugs into one slot on the video card and branches to two outputs.
Have you tried the simple stuff like swapping connectors between the monitor and projector?
Has the projector ever worked correctly with this video card?

If you mean that the video card has two outlets built in then that is a driver issue.

I got it working! Yes, it's a Y-splitter called a DMS-59

First of all, I found out that I needed to use "TwinView"

But my Nvidia driver "nv" was not compatible with TwinView.

So I downloaded the driver that is compatible, "nvidia" driver.

I downloaded it and proceeded to install it. Keep in mind that you have to be in init 3 runlevel. To do this you can edit the /etc/inittab and change runlevel 5 to runlevel 3 and then reboot.

It will boot into command line.

change directory to where driver is located and execute:
sh ./driver_file_name

It will load and possibly ask you a couple of questions, I answered yes to all.

before rebooting I made the following changes using vi on "/etc/X11/xorg.conf" - in the Device section.

Section "Device"
I added the following below board name:
BoardName "NVIDIA GeForce FX (generic)"

Option "TwinView" "true"
Option "TwinViewOrientation" "clone"
Option "metamodes" "1280x1024,1280x1024; 1024x768,1024x768"
Option "HorizSync" "30.0 - 80.0"
Option "VertRefresh" "60.0 - 75.0"
Option "ConnectedMonitor" "CRT, CRT"
EndSection

I saved changes and rebooted. And it worked. It displayed both on my monitor and the overhead projector.

I hope others can use this!