We always run the following: 3 RG-6 for component video (all RG-6 could in your case could be mini coax as needed). 2 RG-6 for S-Video 1 RG-6 for Composite 1 Cable for RS-232 control (or IR control) This covers you pretty well for all sources.
if you use a scaler and upconvert everything you would need a minimum of either 3 coax (component) or 5 coax (RGBHV). Please keep in mind that some plasmas will not accept HD/progressive scan through the component inputs - only through the RGBHV inputs - so you may have to run RGBHV.
And though I'm sure you aware of it, don't forget about using a plasma proof IR receiver if that is your menas for control - which may also means another wire in the conduit.
Finally, depending on the plasma keep in mind that DVI is another way to go but the connector will never fit through a 3/4" conduit (and I don't think you would want to solder one on - at least we wouldn't). The newer plasmas will feature HDMI which uses a smaller digital connector.
We never run anything for audio - which we always run through external speakers and use the plasma as a monitor only.
You probably know all this but I'm just mentioning in case...
