Hi Jim,
There is a thread in the 'Jigs' section of the forum about cutting frets that gives the way that I do fretboard cutting. It depends on having an accurate drawing to start with. I make my fretboards based on a CAD drawing and that jig. CAD is a very accurate way to produce a fretboard. However, as I said above, in the case of a steel, the fret markers are a guide only. That is NOT a license to be sloppy. With all of that said, before I had access to a CAD system here at home I simply used a 24" steel ruler marked to 32nd's of an inch. I got my one at a craft store where they sell quilters supplies. (for the grand sum of $4.50 too!) If you use reasonable care and a fine point marker you will get a perfectly acceptable fret layout. As you will discover when you start actually making your first fret board, any error in the marking out will jump out at you and can be fixed before it is too late.
You obviously have a computer, do you have access to a good printer also? If you are still having a problem with this after you try it let me know the scale length you are going to work with and I will post a center line drawing of fret spacing for you. I will also let you know, at that time, how to print it full size on a standard printer.
Allan.....
EDIT: Jim, I have started a new thread in the 'Tools and Shop' section of the forum to cover some of this.
Here