ahh, music theory, an almost lost value in rave music. tell you what, i finished a music degree with a good mark, but im still baffled by most theory..
it seems very daunting when you're an absolute beginner, as there so much to learn. but it is not necessary to know everything. just like there's no need for an author to become an linguistics professor to write a book, there have been many great performers that couldnt even read music, just knew how to play their instruments. and of course the countless electronic producers who have no idea what a Cb7sus4 is..not that is necessary, just saying..
the good thing about composing according to musical rules, is that you can go as deep or as superficial as you want. especially for more novice musicians, you can start writing music by just following a key's notes, and then go into learning chords, roman numerals, substitutions, dissonance, resolution, the rabbit whole goes very, very deep.
here's a few links that i found invaluable whilst studying:
http://en.wikipedia.org/wiki/Music_theory
good ol' wiki has some good explanations on each area of music theory. make sure to check all the subjects on that page.
http://www.looknohands.com/chordhouse/piano/
similar to Woodz12's link, interactive piano roll which shows all keys and chords you'll ever need.
http://www.good-ear.com/
essential ear training website, with audio and examinations of varied levels.
http://www.musicroom.com/se/ID_No/011274/details.html
http://www.musicroom.com/se/ID_No/011275/details.html
these two books are the standards for university tuition. well worth to have for referencing.
to be perfectly honest, it is no often that you hear a rave tune with intricate chords or adventurous progressions. i suppose trance makes good use of theory, and styles that incorporate live instruments. but in the more techno orientated styles, many great tunes have been completely atonal or dissonant as hell. if they were written on manuscript they would seem to be completely wrong, if we were supposed to stick within musical rules of keys and limited notes. but the final outcome works fine.
theory isnt very dissimilar to production; they both use particular terminology, they both entail following a very strict set of rules, and in both you can throw away the rule book and create something completely new. i believe that learning basic music theory is the turning point for a bedroom producer getting more serious with his art. so when you spent a few hours reading about compression and equalising, dedicate a few minutes every day to learn a few theory techniques and terms, and to train you ears. it will boost your confidence in identifying samples and acapellas in terms of pitch and key, you'll learn great tricks for creating tension in your tunes, and it will make you a more complete musician.
(blah blah blah, i shut up now...)