Level 7: No password box in that level. Check the source and take a second look at stuff which might seem random at first.
Level 4: Since this level has a sort of 'you won't ever figure this out if you don't already know it' style here's a vital piece of information:
Morse
Level 6: Check the bottom of the page and check the page source. Use Google to your advantage.
More legal hints are given on the official forum here:
http://forums.gameservers.net/showth...threadid=22002