Learn to love your Bézier¹ vector curves/paths, and everything else will follow and flow. ;) (To get started, why not play ‘The Bézier Game’? › http://bezier.method.ac)

¹ http://jasondavies.com/animated-bezier/, http://mathworld.wolfram.com/BezierCurve.html,

Illustrator's tracing tool is pretty awesome for getting things started. It won't be a 100% accurate, at which you start hammering away at the pen tool.

Checkout The AGSC they have a few good tutorials on the lettering process including digitizing the lettering.

If you cleaned it up enough in photoshop you could take it into illustrator and live trace it as Ege suggested depending on what level of detail you want, you'll get better results if the image that it is trying to trace is larger also.

Hope this helps.

If you have an iPad then Adobe Ideas is very useful

There are tons of hand lettering resources online. One of the best one-stop-shops for tons of resources (on everything, especially hand lettering) is Skillshare.

Here's a referral link: http://skl.sh/179CLbJ If you use the referral link to signup you will get 1 month of free membership, so it's a good way to try out as many classes as you like and decide if you like Skillshare.