I tried lighting my aquarium with a 70w metal halide lamp and it was not bright enough (still quite dim and not very effective). While searching on the local classifieds, I found this:
http://minneapolis.craigslist.org/ram/for/5707293300.html
This would be perfect because I tried a 175w halide instead and it was much nicer. So my question is, could I shorten this to 36'' and use 1 or 2 lamps instead? Also, do these use 3 lamp ballasts or individual ballasts?

Also, can anyone tell what it is made out of? It looks like plywood to me but I don't think that would be heat resistant enough for this.

Looks a lot like painted plywood on the outside, with painted metal on the inside. You can always add more cooling, or get more air conditioning.

I am thinking of getting it and taking 1 lamp and ballast out and putting that in a smaller enclosure. Plus that way I can put this thing back together if I get a larger aquarium (which I plan to do soon)

And are you sure that you are using the right color/spectrum bulb? Water can be tricky if you don't have the right K.

I think its separate ballasts. There is little sense in doing it otherwise (a combined ballast may be marginally more efficient but way more expensive, to an extent that cannot be justified)