This receiver is many years out of date, but should be able to handle component video from up to two of your sources.
http://manuals.harman.com/HK/HOM/Owner's Manual/AVR 140 OM (web) 3-29-06.pdf
I would connect the cable box to the component 1 input on the receiver (video).
Connect the DVD player to the component 2 input on the receiver (video).
The iPod, if you have a 'component' video cable, then you will need to return it and get one with composite video, or you will have to get a new receiver. Please note, many non-Apple genuine component cables do NOT work with iPods. My composite cable for my iPod is 'spotty' at best.
For audio, use either coaxial or optical digital audio inputs on the AVR-140 receiver for your DVD player and cable box.
For the iPod, just use the analog audio inputs. (red & white audio connectors)
You will have to go into the setup most likely of the receiver to assign the component video inputs to sources. So that when you go to 'DVD' it actually uses component 1 instead of just the composite input. Likewise, when you go to TV or Cable, it will use component 2 instead of composite.
NOTE: If your TV is old enough, it may not even accept 480p video over component video, which means that you have to leave it set to 480i output on your DVD player... almost negating any benefit of using component video.