Hi johnnyzou
What is it exactly that you are after here? I can point you in the direction of detailed articles on chords and thier progressions etc, or is it simply an explanation of the chords you state here that you are after.
D7 - D seventh - sometimes referred to as a minor 7th, and I believe the root notes are: D F# A C
This chord leads nicely into a G Major. Try it in Band in a Box.
Em - E Minor - assuming the usual minor scale is used the notes in this chord are: E G B E
Apologies if this isn't the information you were after.