Like bpape said above, it depends on how large your set-up is. bpape's power layout would be overkill for pretty much everyone, but as he mentioned, he will not have to worry about anything.
It is a good idea to run seperate circuits for your A/V gear. Star grounding as bpape did is also a very good idea. It doesn't cost much to do it this way, especially if you are doing it yourself. It basically means to run seperate grounds back to the feeder panel where the circuits originate from. The outlets need to be isolated from the conduit runs, or you just negated everything.
Circuits wise, once you draw out your theater layout, you can get a better idea of the loads that need to be powered. For a small theater, you can probably just tap of another circuit in the basement for lighting. Just add up the total lighting current of each fixture, and you will know your load requirements.
A/V gear can be done the same way, add up the total power requirements and you have the number of circuits needed. Most A/V gear does not draw much power, the larger items are some large TVs, subwoofers and power amplifiers. But you usually do not need to go overboard with the number of circuits. If you just have a small system with a receiver, a single circuit will work just fine, but I would run an extra for future use, or if you want to seperate your receiver from everything else. If you have alot of gear, more is better. Some people go to great lengths to seperate the digital, video from the analog equipment, balanced power, different types of line filtering dependant upon use, etc. You can go as far as you would like, but for most people, just some dedicated circuits are fine.
Another note: I have done power quality measurements on some fairly large systems, and one particular example had many power amps with multipule KW worth of power capability, with the system at well beyond reference levels, pulled peak currents of over 50 Amps from the line, but the average currents could be delivered using a single 15A circuit. Two would be better in this example, but the point is that power delivery with power amps is very dynamic. Where as a DVD player that says it draws 100 watts, will probably draw around or a little less than 100 watts.
Hope this helps....