I agree with the suggestion that your friend should be upfront
with his students; admit that he is learning; emphasize that he
is there to learn, just as the kids are.

I agree that troublemakers should be teamed together in the back of
the class. They will likely prefer to be in the back anyway
and it will cause less distraction for the rest of the class.

I recommend, since your friend knows some HTML, USE IT!
Start the kids using CGI and make their first assignment
getting the computer to say "HELLO WORLD" on a web page.
That will SEEM much, much cooler that just saying "HELLO WORLD"
on a command line.

Start out with something useful and "COOL" then work backwards and
teach the concepts after... this has always been much more effective
for me.