Can you put salary requirements and salary history on a cover letter?

I recommend that you don't. Use the salary discussion only after you've gone through the interview process and both you and the employer realize you are on the short list. Talking about it earlier may cause you to be eliminated sooner than you'd like. Know what the market salary range is like for your position. This will help you tremendously price yourself correctly. I have used this to my advantage and gotten a higher salary (several times) than what I had expected going into the interview, simply by realizing that I was a good fit during the interview and by knowing the employer's need for my skills. The interview really is the final selling place for yourself.

You can but you would be pricing yourself out of the job. You only put it in if the ad asks for it, otherwise always leave it out.

I would recommend talking about salary when you have the most bargaining power. It may be the case that you are rejected for a job on the grounds that you demand too high a wage, but later the person getting the job ends up getting paid around that amount. You always have time to negotiate after they have shown interest in hiring you, at which point it may be costly for them to refuse you.

I don't think salary history is that vital... expected, yes... previous payroll... no.

You can do so.. as some of the employers want this data also..

should not. If they have asked, to begin with you may write "negotiable."

Only if the ad asked you to do so. I like to state mine in the resume. The cover letter is supposed to humanise me. We are not a bunch of qualifications and work achievements only. It should be informal, friendly, relaxed and witty. I find it hard to build rapport with the reader if I had to talk about remuneration expectations at the same time. Put it in the resume, along with job experience.