Even though none of us have ever actually PLAYED the game, Warhammer 40,000 has had an influence on the flavor of the Tech Infantry universe, especially since the rise of the Holy Terran Empire. The grim dark future of WH40K inspired the way we portray organizations such as the Imperial Guard and the Cult of the Emperor. Argus McCall was even named for a character in one of the WH40K novels. The best site for looking up information on the universe of Warhammer 40,000 is the Lexicanum, a fan-run wiki encyclopedia of information on races, vehicles, and historical events.
For more information, see the Lexicanum itself.