Here is how Intimidate works in d20 Modern (and I'd bet my farm on it that they adapt it for D&D 3.5. If I had a farm)
You make your check opposed (gaining +2 for every size categorie you're smaller) you are above the target, or -2 for every size category by a level check (1d20 + target's HD / character level). The target's bonuses for will saves against fear apply to its roll, and characters immune to fear effects cannot be intimidated. If you succeed, you may treat the target as "friendly", as in the attitude (its attitude doesn't actually change, but will behave as if friendly if around you: it will chat, offer advice, offer limited help, and so on. It will not obay you totally or do things that will endanger it).
If you fail by 5 or more, the target may actually do the opposite of what you wish, frustrating you or providing you with wrong info.
Circumstance modifiers apply for good or bad circumstances (you are more open to intimidation if the intimidator holds his weapon at your throat, and is backed up by half a dozen competent looking guys. But that guy half as big as you with the quavering, high-pitched voice will not be so intimidating.)
The part about becoming outwardly friendly wraps up the way intimidate is meant to be (many like to use it wrongly: for example, we encountered a drow scouting party, which was much lower level than we were. Our attempts to solve it without bloodshet failed and they drew weapons. Then I split one of them in half, reducing him from full HP to - 20 or worse, and then made an intimidate check against the others to make them stand still, so I can get what information I want. I succeeded, but they ran away instead of helping me....)