Hello,
Bear with me here, I'm going to try to be very thorough.

I have four PCs connected through a KVM. I have a Logitech Marble Mouse USB Trackball P/N:804377-0000 M/N: T-BC21 .

The trackball has a USB output, but I connect it through the USB->PS/2 adaptor it came with into my KVM. From the KVM, each of the four boxes connected uses PS/2 for keyboard and mouse. My primary box has a removeable hard drive bay, where I swap my W98, W2K and Gentoo install drives (not hotswap) and then fire each one up. The mouse works great on primary:W98 and after removing all logitech drivers, also works great in primary:W2k. The problem I'm having is that in X or even command line (using gpm) for Gentoo on this machine the cursor jumps all over the screen and clicks at random even from the slightest movement of the ball.

My secondary machine doesn't use the mouse, its a text-only box. My Tertiary machine runs Slackware 10.1 with the 2.4 kernel and the mouse works great there. I remember when I tried to upgrade the tertiary machine to kernel 2.6 I ran into the same problem with the mouse, but just settled for staying with 2.4 since I couldn't find a solution. I've tried copying the working lines for gpm and xorg.conf from my Slackware box to the Gentoo one and the problem persists.

If I pull the tertiary machine's Slackware hard drive and pop it into the primary machine, it boots up and the mouse works great through X and command line. So, I know it can't be a hardware problem.

Here's my current xorg.conf file from the Gentoo machine:
Section "InputDevice"
Identifier "MarbleMouse"
Driver "mouse"
Option "Protocol" "Auto"
Option "InputFashion" "Mouse"
Option "Buttons" "5"
Option "ZAxisMapping" "4 5"
Option "Device" "/dev/mouse" #/dev/input/mice
#Option "EmulateWheel" "1"
#Option "EmulateWheelButton" "4"
#Option "EmulateWheelInertia" "3"
EndSection

Section "ServerLayout"
Identifier "Simple Layout"
Screen "Screen 1"
InputDevice "MarbleMouse" "CorePointer"
InputDevice "Keyboard1" "CoreKeyboard"
EndSection


I have tried changing the Protocol to every possible listing found in the xorgconfig menu to no avail. I have tried gpm lines using every possible type, again with no results. In both my xorg.conf and the gpm commands, I've tried using /dev/mouse which is symlinked to the psaux...I've also tried /dev/input/mice, /dev/input/mouse0 and even directly linking it to psaux. Nothing seems to make any difference. I get the same erratic cursor movement in X on the Gentoo machine every time.

I have searched threads on this and other websites and found that most seem to have trouble getting the buttons on this mouse to work as scroll-wheel toggles, but I really don't care about the scroll wheel. I just want the mouse to have basic functionality.

Is there some kernel option I need to change? Have I missed something somewhere? Is it because I'm connecting the USB output of the mouse through the USB to PS/2 adaptor and then through the KVM?

I'm really at the end of my rope here and any contribution is greatly appreciated! Help!!!

The solution seems to have been found in this thread.

Well...
Sort of, I think the issue is a little different...but I'll go try it right now and see what happens.

Thanks!

Well...that wasn't quite it. What actually ended up fixing it was something I had jotted down somewhere around here but I'm not sure which forum it came from.

Turns out I needed to tell the kernel. To /etc/lilo.conf I added:
append = "psmouse.proto=imps"

And it works! Woohoo!
Thanks for the input and thanks to whoever I got that kernel option from! (Sorry I don't remember)