well I have never kept them but I know that you would need special filtration since they only move in the water current not on their own.
Also you would need a tank with no corners since they would just get stuck so no square tanks.
Kreisel aquariums are what you are looking for to keep most species of Jellyfish. As Anthony pointed out, upside down Jellies are the exception but clearly not as visually exciting as most. There are a few books available on maintaining them.
Did you ever get your jellyfish tank up and running? Or, how is the research/dreaming going?
I have kept a couple of jellyfish tanks (one from Jellyfish Art which I don't have much nice to say about) and currently have a 35 gallon tank (DIY kreisel) running with 3 Moon JellyFish (Aurelia aurita) living in it. The biggest trick to jellyfish is to (as mentioned) get/make a proper kreisel aquarium for them! After that they are actually not really all that demanding. Although if you're bad at maintaining a regular maintenance schedule, don't do it.
When I'm not running around trying to get out the door for work, I can post a little more info. If you (or anyone else) have any questions, please post them and I'll do what I can to help out.