How should I list current salary/salary requirements in a cover letter?

I'm applying for jobs in an industry in which I'm not currently employed (due to the lovely economy, I've been forced to work retail jobs for the past two years). Though I am very qualified for the positions I'm applying for and have the required experience, I'm currently WAY underpaid for my experience/qualifications. Several companies have been asking for current salary/salary requirements in the cover letters. I'm pretty confident in giving a salary range or simply saying that my salary requirements are negotiable...but how do I address the fact that my current salary is significantly less than it should be, without reflecting poorly on myself? Do I just ignore the current salary part? Or do I mention what my salary would be if I were working full-time at my current pay?