Only proceed if you want to take the "evil" path. After agreeing to help Mr. Burke nuke Megaton, go into every single house and steal everything (any little piece of junk you can carry). Sell them to the local shops (Craterside Supplies, The Restaurant, Moriarty's Saloon, etc.). If a particular house is locked or you need a key to get into a safe or something of that nature, simply kill the owner of said property and get the key from his or her body. Kill everyone in sight, especially the shop owners because you can get access to their entire inventory, plus the caps that you have already spent on them. Kill every one and collect everything to leave Megaton empty. You should have at least 600 caps. Remember to sell some of the things you gather to the shop owners because you cannot fast travel when over encumbered. This can be done in almost any town you visit. To avoid getting over encumbered, get all the supplies that you can possibly carry, then drop the rest just outside of Megaton. Fast travel to Rivet City or some other marketplace. Sell what you have, then return to Megaton and repeat the process.