In all honesty it's not that a big task.
The better tutorial is the manual SDK.
Ashley wrote a progressive manual once again that tackles the logic behind a plugin step by step.
The "harder" is to learn javascript. And this is a language that is well documented and pretty fun to learn/use. (just follow Ashley's links, and you're set for all the references/guides you need for it)
Add that to the "guided" side of a C2 plugin, it makes it quite easy.
Also, whenever you're in doubt, you can open any other plugin and check its insides, it often help <img src="smileys/smiley1.gif" border="0" align="middle">
If I remember correctly there's a barebone plugin example somewhere (I wonder if it wasn't Ashley who provided it in the former SDK post).
Finaly any question regarding the SDK developpement can be unfrightenly asked in the SDK forum.
Hope it makes you comfortable enough to get started <img src="smileys/smiley2.gif" border="0" align="middle">