I disagree.

There's a lot more that ought to motivate someone for any job, especially when that job is holding public office. People are motivated by pride in their work, civic duty, a sense of purpose, and dozens of other "intangibles". Take a look at all the staffers working for this guy on Capitol Hill (very few make more than $40K despite being among the best and brightest young people in the country). Right now, I've got friends graduating MIT and entering the Peace Corps, and I took at $30,000 pay cut to move from one engineering job to another because I wanted to work on something I'd be proud of.

Anyone whose susceptibility to bribery changes with their salary is already unfit for public office. What you pay is not the only factor in any job. Do you really want a crop of candidates who are "in it for the money"?

Surely you are trying to give these kids a step up in the world, and a way to learn the things theyll need to know to succeed. I hate to say it, especially as an open source fan, but it's gonna have to be Windows. The standard is the standard, as much as it may be a bad one.
When they are in the workplace, they will be using Windows, almost guaranteed. When they get a computer for themselves, or use someone elses, they will use Windows. It may be buggy, and a pain, but thats the way youre gonna have to go.
As for other software... well thats another matter. Take open source and run with it. Open Office, Firefox, Thunderbird, GAIM, GIMP, etc. It'll save you a fortune on liscencing, but it will also give them a look at the program's they'll want. People that are using donated computers wont be able to afford a couple hundred dollar liscence on MS Office or Photoshop... so why bother having them learn it when there are great open source alternatives that run on the OS they'll be using anyways?