A member of another forum posted a horsepower worksheet in a horsepower discussion on another forum. I converted the spreadsheet into a web app to make it easy to play with the numbers.
It is interesting to see how the different variables affect the horsepower needed to move a mass up a hill. I can not attest to the accuracy of the numbers, as all I did was convert the formulas. There are also some interesting links that are helpful in understanding some of the numbers.