wow. that really sucks.
well did you install anything that uses juice, stereo, amp, etc?
sounds to me the reason the battery died is excess parasitic amp draw.
there are two types of parasitic amp draw
good - things that use power to retain memory such as your stereo, ECM. anything that draws power when it rolled off the assembaly line is good
bad - short circuits, stereo equiptment wired wrong so they can stay usefull even though the ignition is off
to test for parasitic amp draw you take a multimeter and disconnect the negative terminal from the battery. put the positive lead on the cable and the negative lead to the battery. make sure the ignition is off and all doors are closed no accessories on.
the draw on my vehicle is acctually pretty high at a whopping .5 amp
generaly you should see about .25 amps give or take (this depends on factory installed things, etc)
if you have draw over 1 amp or more i would lean toward short circuit, if its between .5 and 1 i would try to see if there are any accessorys that are still on.