http://www.amazon.com/Hitman-Collection-Codename-Assassin-Contracts-Pc/dp/B00183MAN8

Does it use steam? If not, what DRM, and how obtrusive is it? Specifically what does it prevent you from doing?

Ahh... why can't we just go back to the good'ol days of plug and play...

Please

I'm not aware of any strange DRM schemes for those games. I think it's a simple CD check. It doesn't use Steam.
What days were those? I think there was always a CD check or special code you had to enter, even for old games. Sure there's some pretty bad DRM out there today with internet requirements and limited installs but we also have http://www.gog.com/en/gamecard/alan_wake now which offers DRM free downloads without any hassle, along with other bonuses.

Yeah, both the first two Hitman games are available on GOG so they are 100% DRM free there, and don't require any disc in the drive so it's quite nice

Games released on CDs were generally without any kind of DRM in the mid-90s, cause very few could afford a CD-burner. But then by 1999 the prices of CD-burners had dropped rapidly and copy protections were used once again, just like they had been on floppies before.

You would probably get a better answer if you asked on the official Hitman forum, I don't think the chances are particulary high that someone else here have the Collection who can confirm or deny it's using the same DRM as the original individual game releases or not. But if it do use the same DRM as the original game releases, it use simple cd-checks thanks to safedisc, securom or whatever.