Re positive discrimination in IT, yes we would choose the female candidate over the equally qualified male one.
As regards what 'positive discrmination' is, the term doesn't seem clear-cut. Wikipedia has it as "the practice of favoring members of a historically disadvantaged group at the expense of members of a historically advantaged group."
adding that it has been "held to be unconstitutional in the United States", but "affirmative action" is legal.
There are some interesting statistics there en.wikipedia.org/wiki/Affirmative_action_in_the_United_States#Class_inequality
apparently being black is equivalent to an extra 230 points on your SATs (and as such actually beats the 'old school tie' alluded to by dittany, in the form of children of benefactors, who 'only' get +160) and the black acceptance rate is twice as high at MIT and 67% at Harvard as the general acceptance.
Incidentally you don't get many black people in IT either, the only one I've worked with said he owed his success to the year he spent at private school courtesy of Margaret Thatcher's assisted places scheme. His mother was a motivated single mother from Dominica, and obviously supported him. Curiously enough he said that despite having plenty of money to afford it, he wouldn't send his son private because he doesn't think private education is entirely moral. I think he prefers the 'buy expensive house near posh state school' approach.
My understanding is that certain employers have tried various 'fair' ways of encouraging minority applicants, for instance recuritment days at Muslim and black festivals for the police, but it didn't produce the desired results so they do in fact choose discriminate against the majority (i.e. white male candidates).
Obviously such places (the BBC has a stated goal of achieving something like 15% ethnic minority staff, which is above the proportion in society) are the exception rather than the rule, but I do think that employers are aware of discrimination legislation - if you are a big company a 'golf buddies' recruitment process will end up with an office full of men, which would be pretty good prima facie evidence of discrimination. So I'm sure that this does figure in the recruitment process at some point.
Especially given that the gatekeepers, the HR department, are likely to be the most right-on department in the company, not to mention one of the ones with the highest proportion of female staff, for I guess the same reasons, in reverse, that IT is dominated by men.