To find out if you can remove them, crawl under the car and look for hex bolts or something. To polish them start with a Dawn wash to get the crud off (brillo would also work), get a bunch of different steel wool grades, and some metal polish (I use Mothers, use what you like), polish the crap out of them with each grade of polish-soaked steel wool, repeat until shiny (may need haevy cut paint cleaner), once shiny enough you put a few good coats ( :hah 1000) of your favorite sealant (preferably one with which you could have on your car for several months with no ill effects (read: DURABLE).
If you do this correctly, your exhaust tips should come out mirror-like. Have fun.
By the way, it takes a while, so bring a soda or twelve to keep you hydrated.