I went for many a year doing what you're doing BigDaddy. The key is to learn the notes on your fret board if you haven't already. I would learn all the note on all the strings to at least the fifth fret, and then all the notes on the 5th and 6th strings from 0 to the 12th fret.

Now as you listen to the song, first find the key as suggested above by just trying to find that note on the fretboard; that's your tonic and that's your main chord. If as you play the chord to the song it sounds off, try the minor or the seventh chord. Then listen for when the change in the tune calls for a new note/chord and so on.

The easiest way to learn tons of chords, aside from the basic open ones, is to learn the barr chords rooted on the 8th and 5th frets (at least for starters) So for example the open E shape barred at whatever note on the sixth string renders twelve major chords. Pick up your pinkey and you've got twelve seventh chords. Pick up the middle finger and you've got twelve minor chords. Pick up both the pinkey and the middle fingers and there you have twelve minor seventh chords. And remember, that's just the 6th string.

Hope that helps. There are lots of web sites but a good book might also be of some help I like Ralph Denyer's "Guitar Players' Handbook". Good luck. sb