A common misconception is that w00t stands for "wow loot" or "we owned other team". These are, in fact, bacronyms. w00t originated from the music culture in the early 90s, such as the song "whoot there it is". A more detailed etymology of w00t can be found at its wikipedia entry.
w00t, pronounced to rhyme with boot, is almost universally used as an expression of joy
Originally derived from "woot" (win over opposing team), evolved into (we owned the other team). Then "woot" was bastardized into "w00t" Now can commonly be used as a general expression of happiness.