Not sure of the other things, but as for the double boiler question, here's a few to give you an idea of what they look like: http://fantes.com/double_boilers.htm You basically boil water in the bottom pot and the "pot" on top cooks from the steam given off by the bottom pot.
Well, one thing that might be handy if you like to cook with garlic is a garlic press...I just got one as a wedding gift (one that actually works too! LOL), and I love it. I can't remember the brand name, but if you're interesed, I can let you know when I get home....