Sherri -

Quarantine tanks usually tend to be very basic in setup. If it is just for fish and inverts, you really only need a regular flourescent bulb as fish don't require much lighting. Also, it is better to have a bare bottom tank as it makes it easier to clean and you don't want the live sand and rock to absorb any medicines you may have to dose. All you need is a heater and a filter of some kind. Filters can be a simple sponge filter or power filter. For a 30gallon, probably add a power head as well for circulation. Most of the time, people don't keep their quarantine tanks set up full time. When they know they are going to purchase something, they get it running in advance. When the tank is not in use, you can put the sponge filter in your main tank sump to keep beneficial bacteria in it for when you need it again. You take water straight from you main tank to fill it up so that the water is of the same composition. Set your heater to keep the water at the same temp as your main tank as well. You still need to acclimate the livestock to that water as it will be different from what it was in. You can put some kind of fake coral or plant in the tank so they have somewhere to hide/feel comfortable at.

Hope that helps!
Chris