One perspective is that negotiation of schedule and resources is often nothing resembling estimation but is a political game. Ed Yourdon's book "Death March" has a chapter about Negotiation .

http://ptgmedia.pearsoncmg.com/images/013143635X/samplechapt...

There's a list of "negotiation games" that, sadly, you'll probably recognise. And a bit of more practical advice:

>> The problem I have with “estimate” is that I understand
>> the word to mean, “best assessment knowing what is known
>> at this moment and what can reasonably be predicted about
>> the future.” From experience, what I have seen happen is
>> that once an estimate is published,it becomes a rock
>> solid commitment representing the maximum amount of
>> resources needed to accomplish the project phase or the
>> entire project.

> Unfortunately, there’s an uglier aspect of the political
> negotiation when you introduce the plus-or-minus
> qualifier into your estimate: You’ll be accused of
> uncertainty, wishy-washiness, weakness, or even
> incompetence. [...] What senior management really wants
> is a firm commitment — a promise that the project will
> be finished on a certain deadline, with a budget of a
> certain number of dollars, and a staff of a certain size.
> This gives them the enormous luxury of (a) no longer
> having to worry about the problem for the duration of the
> project and (b) having a convenient scapegoat to blame if
> the promise is broken.

> Jim McCarthy, in his excellent book, Dynamics of Software
> Development, suggests that the project manager needs to
> confront this head-on and persuade the customers and/or
> senior management that they need to share some of the
> burden of uncertainty [around schedule, cost, resourcing]
> that the entire project team will be living with on a
> day-to-day basis. Thus, the project manager effectively
> says to the customer or the senior management group,
> “Look, I don’t know precisely when this project will
> finish — but since I’m the project manager, I’m far more
> likely than anyone else in the organization to figure it
> out as soon as it can be figured out. I promise you that
> once I know, I’ll tell you right away.”

> Only a manager with a lot of self-confidence, and the
> ability to walk away from the assignment, has the
> chutzpah to say something like this in the politically
> charged atmosphere of a death march project. The time to
> say it is at the beginning of the project; after all, if
> the customer and senior management do not respect your
> ability as a project manager, and if they don’t realize
> that you do have a better chance of knowing when the
> project will finish than anyone else, then why are they
> putting you in charge of the project in the first place?
> Are you being set up as a scapegoat? Are you going to
> be a “puppet manager,” with all the decisions being
> made by other political manipulators in the
> organization? If so, now is the time to get out!

> Similarly, if you’re a lowly programmer on the project
> team and you see political games like this, it may be a
> strong indication that your project manager (a) doesn’t
> have the confidence to believe in any estimate that he
> puts forth, (b) doesn’t have the backbone to stand up
> for himself and for the project team, and/or (c) has
> gotten himself into a political situation where all the
> key decisions will be made by people who are not
> directly involved in the project. Again, this is a
> strong indication that the project is doomed; and
> before you get too deeply involved, it might be a
> better idea to seek greener pastures.

Refusing to be pressured into emitting on-the-spot "estimates" that will be regarded as commitments is a useful life skill. Teach your new hires: http://www.dadhacker.com/blog/?p=2267