The audience doesn't officially learn that Stane is secretly trying to kill Tony until the third act or so, but the movie actually reveals it way earlier, right after Tony gets back from being tortured in a cave and announces that he doesn't want to build weapons anymore. After a hilarious montage of Tony injuring himself in his workshop with his new Iron Man equipment, he comes upon Stane playing a baby grand piano, because villains are irresistibly drawn to giant Steinways like bugs to lamps.
"Oh, don't mind me. I'm merely diddling around with 'Movie Spoilers In D Minor.'"
If you know your 18th-Century composers (you do, don't you?), you'll recognize the piece as Antonio Salieri's Piano Concerto In C Major. If you also know your 1980s movies, you'll recognize Salieri as the guy who killed Mozart in Amadeus, a movie about a bitter older rival insidiously destroying the young, brash upstart composer. Throughout the film, Salieri is tortured by the fact that he can't do work on the same level as the young genius, just as Stane bemoans his inability to reverse-engineer Stark's invention. ("Tony Stark was able to build this in a cave with a box of scraps!")
Luckily, Tony didn't also posses the world's most annoying laugh.