djasper99,
You can use just about anything that holds water as a sump. It is pretty much just a body of water for you to put the stuff that you don't want people to see in your show tank, i.e. your protien skimmer, heater, pump, etc. I have seen people use 10g tanks, rubbermade containers, trashcans, 5 gallon buckets, a bunch of monkeys with pails (okay, maybe not that last one). The only thing you will need to worry about, is putting in some sort of bafold so that your pump does not suck up air bubbles from your protien skimmer or overflow. This just means siliconing a piece of acrylic to inside whatever you decide to use for a sump. I hope this helps.
Mike