The post mission 3 hang caused alot of people probs after the US release. Most people say it is a sound problem - usually having a DivX sound driver installed, but just generally not having the standard windows sound driver as you primary driver. Do a search for posts (from anytime, not just last 30 days) about mission 3, theres some detailed advice.
However no matter what i did it wouldnt fix, so i reinstalled windows. Still, it was easily worth it.

P.S. If you do reinstall back up your saves or you'll cry like a baby like i did.

Red, you tried the ramming method as well?

I have heard that it sometimes helps, because the game doesn't actually sees the killings as done by your hand. They are destroyed and you can continue with the mission.

I didnt try the ramming method, i got stuck really early on (a day or 2 after release) and i think the ramming method was but a twinkle in someones eye.
I'm still suspicious of the sound fix for this tho cause as i have ranted on other posts i had the sound problems, uninstalled divx which fixed them. Then i still got stuck after mission 3.

It probably sounds crazy but i'm sure it is no accident that having divx buggers you up. Remember microsoft got in trouble cause there was encypted code in windows 95 or 98 that deliberately screwed you up if you were dual booting windows and OS/2? (Allegedly)