The following are cheats. Do not use them unless you want to spoil the game

Endings Guide
Every Possible Point (Game Players)
Inventory Objects
Good Guy Points
Infinite Points
Getting Passed the Alien - The Easy Way
Infinite Good-Guy Points

The following are some cool things to try. Trust me, they won't spoil the game.

Secret Room of the Programmers!
The amazing, never-ending, Rook conversation!
Tex Murphy: Bird!
Close the Door and the Room Disappears!
A Y2K Slip-Up By Access!
The Time Traveling Detective