for speaker wire, you really do not need to buy conduit.
I ran all my wires through the ceiling before I put up my drywall, just drill 3/4" holes through the joists and run your wires where you need them to go. Make sure you intersect all electrical (for lights etc) at a 90 degree angle if you HAVE To intersect. It is advised to stay at least 24" away from any parallel electrical run.
The only reason to use the conduit would be for video to your projector (in case in the future you want to add more video cables).
Even if you don't plan on a full 7.1 setup, wire for a 7.1 setup.
You can get most of your supplies at monoprice.com, including all your speaker binding wall plates, HDMI wall plates, and component video wall plates. Measure out how much wire you need for each run for each speaker, add them all together, and add about 15-20% extra. I got all my speaker wire thru bluejeanscable.com (Belden 5000UE (Gray jacket, 12 AWG). Comes to $0.38/ft for excellent in-wall rated 12g speaker wire (you will want to use all 12guage for your runs).
As I mentioned, monoprice.com is the best for all your video stuff and interconnects (wall plates, etc). They just got in the new HDMI 1.3a cables...however, if your new projector does not accept HDMI 1.3, it would be useless to use the new cables...just use their regular 22guage HDMI cables (they are stinkin' thick too), and they will pass 1080p thru them flawlessly. MAke sure all your stuff is in-wall rated.
For your riser, Go here
Riser Height Calculator.
Thats all I got for now...thought I would throw my 2 cents in. Also, for soundproofing, nothing sound proofs better than mass, don't think a suspended ceiling will do anything, because it won't. Green Glue is an awsome way to go about soundproofing, between 2 layers of drywall, it will provide up to 60db of soundproofing (I think, check out their website for more solid stats and advise for soundproofing).
Edit: Forgot about your electrical runs:
1. at least 1 20a run to where your Amp and electrical gear will be.
2. I ran a dedicated 15a line for my sub.
3. I ran a dedicated 15a for my projector (this will increase bulb life because it doesn't get fluctuation in power).
4. I ran a dedicated 15a to all my lighting and other general purpose electrical outlets in the room.
I probably went overboard for a little 14x16 room with 4 dedicated runs, but better to be safe than sorry.
