<font color='#000000'>I have no experience with the belden wires, So I can't offer any advice on them.
With coaxial cabling, the center conductor is the positive lead.
With twisted pair wiring, i'd say just choose one to be positive.
the 1/4 inch plug should have a tip contact and a larger 'shaft' contact, the tip should be your positive. most 1/4" plugs are made to work with coax type cable as well, so it's almost as easy as the rca plugs if not easier. Stereo 1/4" jacks are more difficult, I always get messed up on those.
For soldering, heat up both parts with the iron and let the solder flow into them. Soldering is more than just gluing, it's a metallurgical bond between the wire and your plugs. You might want to get a hobby vise to make this task easier or if you have a friend who has one, borrow it. A solder joint should take no more than a few seconds. If you have a broken walkman or other electronic object, you can always practice removing a component and reinstalling it until you get good at it. That's how I learned to do it.
Here are a few links on soldering for you:
http://www.geocities.com/ammarini/soldar1.htm
http://www.aaroncake.net/electronics/solder.htm</font>