If you would like an example of the finished product, take a look at "my photos". My TRD Exhuast originally came with polished tips only. But, because you can see a considerable amount of piping if you're driving behind the truck, I decided to polish what was not polished originally. Now, it looks like chrome.

I started out by sanding them with an orbital sander, and 220 grit sandpaper. I sanded them down untill I saw an even finish of metal (they were kind of brownish colored and very grimey when I started).
Then I sanded them with 320 grit sandpaper on the orbital buffer. This kind of gave them a satin look polish.
Then I wet-sanded them by hand with 600 grit, and then 2000 grit wet-or-dry sandpaper. (the 2000 grit probably isn'nt necessary, I just did it for kicks)

Then I polished them with a small Craftsman buffer, and a wool pad, and some heavy duty rubbing compound that you can get at an automotive paint store. This really polished them to the chrome finish, but left minor scratches.
I finished off with Mother's Metal Polish on the buffer, and this removed the small swirl marks.
Then buff to a mirror finish with a dry, soft rag/towel.

It only took me about an hour of work, and it really improves view from behind.
Have fun.