Cubasis, what your heard isn't true. Heros can level far far beyond the amount of skill points they will use, it will simply stop giving you skill points. niro is right. Heros can't level past level 5 on ONLY creeps, unless it's changed in gameplay constants (the advanced tap to the right of file, edit, veiw... etc.)
Also, niro, nice tut. I see a lot of newbies lost in more advanced tuts and people always have to stop and explain everything from scratch to them... If we get some more 'to the newbs' tuts out there, maybe this will stop happening.