I have just uploaded Excel Star System Habitable Zone Calculator to the downloads area.

If you know a star's stellar class, it's Apparent Magnitude, and how far (in parsecs) the star is from Earth then you have all you need to calculate the inner and outer bounds of a habitable planetary orbit around that star. Here's a simple Excel spreadsheet that does the math for you.

You can find the file here in the downloads section. Please use this thread for comments.