How many dedicated circuits to run HT/2ch system..

Keep in mind, it's alot easier (and cheaper!) to run an extra dedicated line or two now than to add one later. If you're still at the rough-in stage, go big early! Ask the electrician to run 10 gauge wire for the amps.

I did the same not too long ago. Unless you plan to have really large amplifiers with lots of current draw as AVguy mentioned, this is how I set up mine:
All circuits 20amp (cost pennies over 15amp circuits)
1 for amps (more if you need them)
1 for video (RPTV and SAT)
1 for pre-amp/sources
1 for sub if it's far away from the other outlets
Keep all other general outlets on a sep circuit
Keep all lighting on yet another circuit especially if you will use dimmers.
And, have the electrician put an outlet in the floor! Yep, middle of the room, back toward the seating poistion. Great for remote controls, cordless phones...etc.
You can put one in the floor near where the amps will go too if you intend to have the amps out near the L/C/R speakers.
I used metal boxes, BX wired and hospital grade outlets. Some will say spend more on the outlets for "audio grade". I'm skeptical but, it's only money.
Enjoy!

As far as the amps go,it depends on how power hungry each of them are. --Maybe a line for each? In any case no more than 2 per line. Check your amp specs.--looking for maximum current draw.A 15 amp line can supply 1875 watts;but one would never ask more than 1200/1400;--need that headroom.Your tv--What kind?? CRT projector--?? It's own line. LCD projector--?? you could run 4 on the same line--(My way of saying they don't need nearly as much)--RPTV--??--Typically no more than 400,draw. Those are the "power hogs". Also, their location has to be factored in. A projector would need the line at the rear. A RPTV--at the front of the room. Lastly; a line for dig.--a line for analog for the front end. Maybe one exta line for future needs-- "headroom"--??