get a decent text editor I use nedit on linux and it's much better. Because if your script crashes maya (which it will trist me!) and you haven't saved your script you can kiss it goodbye forever! I always work in a separate app and then source it in before I run it each time.
Also you can't really step through, the best you can do is put a whole bunch of prints in there!
Welcome to the world of MEL it's a world of pain believe me!!
Alan
Technical Director - Framestore
Currently working on: Your Highness
IMDB