A brief introduction to key financial concepts is available at www.teachmefinance.com.

How much do you need at retirement? Check out the "Money/Retirement" link at www.about.com.

For a downloadable, Windows-based financial calculator, go to www.calculator.org.

Why does the Rule of 72 work? See www.moneychimp.com.

Learn more about using Excel for time value and other calculations at www.studyfinance.com.

Time value applications abound on the Web. See, for example, www.collegeboard.com, www.1stmortgagedirectory.com, and personal.fidelity.com.