How do i use it so my tv programming is in surround sound?

If the Comcast cable box has an HDMI output, it should connect directly to one of the TV HDMI inputs. Then connect the LG DVD unit HDMI output to the second HDMI input of the TV. Use two HDMI cables. Do not buy the expensive Monster HDMI cables. If you have already done so, I recommend you take it back for a refund, then buy the low cost HDMI cables which will work just as good and then you can bank the savings toward a new Porsche Boxter!! Now we have the video connected from both the cable box and the LG system.

Now--what do you do if the cable box does not have an HDMI output--just use its component output and your component cable (red, blue and green) to connect to the TV component input. This will still get the video to the TV and good HD pictures. Hum--do you have an HD cable box? You did not say and I just assumed that you did since you got the HDTV. If not, let me know with a follow up question and I will assist in that area further.

Now for the audio connections--The DVD player will not need any connections since it in the LG unit. The sound will come out the speakers when you start playing the DVD. The cable box is where we get the TV audio to feed the LG unit. If the cable box has an optical output, use an optical cable (again the low cost one)and connect to the optical input on the LG.
This will get the TV audio to the surround system. If no optical output, use the red and white (left/right) audio connections and connect to one of the two the LG audio inputs. To hear TV audio on the LG speakers, just switch to that input or the input associated with the optical input.

To watch DVDs, switch the TV to the HDMI input to which you connected the LG unit. For TV, go to the other HDMI input (or component input).
Switch the LG to the audio input to which you connected the cable box to get TV sound.

Hope this gives you food for thought. If so, and you have more questions, just come back in with a follow up.