Little intro to keys--hope this helps a bit. For starters, here's the notes in each key:
C: C D E F G A B
G: G A B C D E F#
D: D E F# G A B C#
A: A B C# D E F# G#
E: E F# G# A B C# D#
B: B C# D# E F# G# A#
F#: F# G# A# B C# D# E# (yeah, E# is the same as F, but this keeps with the cool alphabet scheme...)
Db: Db Eb F Gb Ab Bb C
Ab: Ab Bb C Db Eb F G
Eb: Eb F G Ab Bb C D
Bb: Bb C D Eb F G A
F: F G A Bb C D E
Take the 1st, 4th, and 5th notes in each of those keys and make a major chord using that note as your root note (the lowest note in the chord). That's why you hear "I IV V" progression thrown around quite a bit. To find the minor chords, do the same thing with the 2nd, 3rd, and 6th notes (but with minor chords, obviously).
Each key has a "relative" minor key associated with it. To find which minor key corresponds to its major key, just look at the 6th note. For example, E minor is relative to G.
Start with that, and let me know if this is worth anything to the people who have never really done much with theory.