Tutorial on transition and preloading external files - problem

The tutorial is very good but i think there is something wrong: i think the preloading of the files doesn’t actually work. I tried to set a connection speed and i noticed that even with the slowest one the preloading sequence acts as if the files are already loaded. I’ve been trying to figure out what’s wrong the whole day and i’m starting to give up. I think the problem is within this peace of script atached to the content movie clip:
if (!loaded && this._url != _root._url) {
if (this.getBytesLoaded() == this.getBytesTotal())
The condition must be always true. Actionscript is a bit new to me and i just can’t make it work.
I have one more question: Can somebody explain to me what’s does the first condition actually mean and what does Flash do if the whole condition is false?
I deleted " !loaded " and " this._url != _root._url " one at a time just to see what happens but i still can’t understand what is going on.

I’ll be happy to read what you guys think.