1. Start a new game and play as usual, giving the other empires time to build up their resources.

2. When you're ready to steal resources (as you're running low on resources yourself), save your game, quit, and then reload another empire to play as.

3. Once you have loaded your alternate empire, go to the Diplomacy menu. Send the resources from this empire to your "normal", default empire.

4. Save the game, quit, and reload your original empire. The resources sent from the alternate empire should now be there -- you can repeat this as much as you want.