Drawing in Flash

So I have been learning Flash MX 2004 and I have come to a relization that I don’t know an eighth of what I should know.
I went to www.seanjohn.com I loved the flash Intro and I want to create something like it. The part that I don’t understand is how to make it look like the words are being written. For example his logo has a signature and it looks like the signature is getting written as you watch it. I relize that it has something to do with Masking layers. But I haven’t figured it out. Please if you have ever seen a tutorial that touchs down on that subject please post me the link where I can find it. Thanks. Happy Flashing!