Game starts fine, no crashes but as soon as I get to the first interactive moment in Tex's office, the mouse is unusable. For only fractions of a scond it shows up but they are only glimpses. I can open the panels on the top, left and right, but can't click on anything once they are open and you can't see or use the mouse/cursor.
It's not that it is invisible either; even when I know it is over something becuse it blinked in for a second, it still won't click on it.
Right clicking and holding allows me to move about the room, but I can't interact with anything once I stop.
I have an HP Firebird 802
Intel Core 2 Quad CPU Q9400 @ 2.66GHz
4 GB RAM
64 Bit Windows Vista Home Premium
I shut down everything the program mentioned except "Start" which was a yellow, not red item.
I also ran UAKM and Pandora Directive without the slightest issue.
Any suggestions?

I get that you can't even use your mouse to change the preferences in the game menu?
If you can use it for that (before starting a game) go to Config->Preferences and disable Trilinear and Mip map.
If you can't access the menu with your mouse go to your game folder, open the file tex.ini and change the lines
Trilinear=1
MipMap=1
Into
Trilinear=0
MipMap=0
See if that helps. What's your graphic card and your drivers by the way?

Unfortunately, that did not work- although I really do appreciate your effort in helping me out. . I do have a cursor prior to being in the game, so I deselected Trilinear and Mip Map as you suggested. Now, I can hit the buttons on the 'in-game' menus (top, Left, Right) but I can't see the cursor. It will still not show or function with the gameplay screen.
To your last question, I have dual Nvidia GeForce 9800 S cards.
I sent this to gog support last week and they wanted the DxDiag which I provided last Thursday. They have not yet responded.

in the tex ini file also change - lock video -1 to just 1, this helps with mouse problems but usually curser trails, wouldn't hurt to try it. Overseer has real problems with dual anything (cards & processors) just run one processor & 1 card

If you have a dual graphic card, try to disable in Nvidia panel one processor.
It can fix the problem.