Originally Posted by: ZakJenkins

V7 is the dominant chord of a key, diatonically speaking. V is a roman numeral for 5, because it's built on the 5th degree of a scale. A V7/V is basically just (In C major) A G7(G,B,E,F) To a G, (G,B,E) which makes a small difference, depending on how it's used. No D's anywhere, unless you meant II7/V, which is a nice cadence.

i hate to be the bearer of bad news, but a secondary dominant is the idea that you are building a DOMINANT chord off the DOMINANT tone in whatever key you are in. so...in C major, you are right...the DOMINANT tone would be G. however, the DOMINANT tone of the DOMINANT (repetative, i know) would be D.

so light, you where actually very right in assuming that it would be D7. while you could simply call that a II7, the reason we don't call it that is becasue it makes no sense in a theoretical kind of way. in a major scale, we don't find a major II chord, so what we have to do is relate it somehow to another chord that makes sense, and in this case, its the V chord.

but i think others may be right on the relevance of this to pop music.

if i understood you correctly, though, you wanted to make interesting orchestral arrangements. there's nothing better than learning a bit of classical mumbo-jumbo, if you ask me :D