The screw and glue method is your safest bet. It's 100% overkill for a stand, but that's always good :P. Your house isn't even glued, and only uses nails. For a 20 gallon using 2x4's is pretty overkill, but if you don't need much room under it then it's probably the cheapest and easiest to do. If you're using one of the many guide online pre-drill your holes if they are close to the ends of the wood, then the wood will not split.
Easiest method is this:
http://www.aquariumlife.net/projects...m-stand/56.asp
basically build 2 rectangles the size of your tank and a few 2x4's to hold it up.