I'm pretty sure that the Troll part, by itself (sans the half-dragon template), means that you take Six, which is your hit dice, and then<em>add the plus five level adjustment</em>, to get an effective starting level of 11.  That sounds sick, but it's actually kind of reasonable given your massive Str. bonus, regen, rend attack, etc. etc.<br/><br/>SO, you'd have to add the half-dragon template cost to 11, and then whatever you had left over could be actual class levels.