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.

EDIT: I've made some slight changes. Actually, I simply added extra formulas. Now, you can enter the stellar class and the absolute magnitude, if you have that information. Also included output for Orbital Period and Rotational Period.