No worries mate, I was in the same situation as you not long ago. It sounds like it's as much a co-ordination thing as an articulation thing - and many people start off with this problem. Making your chord sounds cleaner is a bit of a drudge - it basically involves a hell of a lot of fine-tuning and practice of your finger positions. Play the chords that are giving you trouble (barre chords, for example) and keep adjusting your finger positions until you can strum the chord and hear all of the notes ring as clearly as possible. Practice taking your hand off the fretboard and replacing it in the proper position, and also moving your hand around in various chord positions.

Most importantly, FORGET SPEED TO BEGIN WITH. It sounds like you're a Metallica fan :cool:, but if you are eventually going to play like James Hetfield, it's best to start slow. Make sure that you can play various chord changes as well as possible before you build up speed. That way, when you eventually begin playing at the same speed as the recordings in question, your guitar work will sound crisp and precise.

Making chords "fit" into songs is a bit more fun. Get yourself a metronome (or go to the online one - sorry, I forget the web address :o), set it to a slow tempo, and practice playing a chord progression along with it. Slowly build the tempo up to the speed of the recording as you improve your fluency. When you start writing your own stuff, it also helps to get a drum machine, so you can base your rhythmic ideas on the drum beats.

I don't know whether that was of any help to you, or whether I just told you a heap of stuff that you already know :o, but I hope you were able to make some sense of my gibberish.