I wouldn't bother trying to protect your script all that much. Regardless of what you try, someone is going to be able to crack it. If Microsoft can't prevent people from hacking their programs, you don't stand a chance.
Also, how much effort do you want to put into this, seeing as it probably wouldn't be worth protecting all that much anyways? You're not going to be creating the next Windows OS in AutoIt, so whatever time you put into this effort is probably worth more than the software will get you in the end.