I separated my 1/2" OD copper tubing into two segments, and took the 35' one to convert to an immersion wort chiller. I generally followed the instructions from this All About Beer page.
Word to the wise: bending the 90 degree angles is tough without the spring tubing bender - I put a decent size crimp in the inlet run but was able to recover it for the most part. (I'm going to play it off as an intentional attempt to introduce turbulence in the water flow so the heat can transfer more thoroughly.)
I used a paint can to give me a guide for the coil diameter. It's a little too small but I didn't wrap right up against it so the effective diameter is a little larger than the can. The coil has about two inches of clearance from the side of the boil kettle, which is supposed to be right.
It's pretty ugly but I tested it and it doesn't leak from the hose connections.
The completed chiller and the "turbulence crimp":