The Vedas contain Philosophy, the Upanishads are like commentaries/expositions, and you might also want to read later explanations of the Upanishads (Sankara springs to mind instantly). It's difficult to find translations or study guides that don't have a bias of one sort or another: either the Vedas perfectly predicted every snowflake that ever fell (and much more), or they're nothing more than the babbling of primitive peoples. If you understand the Vedas to be poetry, the Upanishads to be closer to prose, and commentaries on those to be "textbooks" of Vedic philosophy, then you might be able to acquire a balanced view of the whole lot. I will stress now, though, that the more rigidly you try to define what is said by the Vedas, the further away you'll come from understanding them. Like the I Ching, they can be read in very many (and conflicting) ways, though each reading is accurate and true within its context.
Edit: stay away from Muller and Griffith.