How do the wick holders work? I've had no luck with floating wicks in oil lamps and haven't been able to rig up anything on my own from wire. What should I be looking for? (Do they stand in the oil or attach to the rim of the cup?)

The wick holders stand in the oil. You slide the wick into the holder. I fill the cups first and then place them in the oil, but I can't see why one wouldn't be able to pour the oil around them. And they work very well - you can put in as much or as little oil as you need, and there's no need to put water in the bottom. All of the oil is consumed, with no scorching, so it's better all the way around. (And the old wick is easy to remove - if it doesn't slide out when you take the holder out of the cup, you just use a match to push it.)