Well, for starters you'll need a scanner! If you don't already have one, you can pick up a decent flatbed scanner for between $50 and $100 (the top rated one on NewEgg
is $79.99). Most scanners come with at least rudimentary software for working with scanned images, and that Epson model from NewEgg is supposed to come with a solid, if limited, scanning utility.
Next, after you've scanned all the letters and have a big pile of images, comes the burning part. Lombardi Rahm mentioned ImgBurn for burning CDs, and I also recommend it.