I did this to my stock KX250 pipe.. It turned out very nice! It looked similar to the factory CR250 pipes that we saw on Carmichael's bike this year.. Nice and glossy, and the harder you ran it the more it blue'd out.
I used aircraft coating remover and a brass wire wheel on a cordless drill. It takes some time and elbow grease, expect to ruin the brass wire wheel, but it turned out very nice. I used the high-temp clearcoat paint, giving it about 4 or 5 coats.. It only lasts about 2 or 3 rides until roost begins to blast it off at the front, and it will get rusty when it gets wet real fast. The rust always cleans off, but to save yourself some time/trouble, just spray the whole pipe down in WD40 after you wash the bike, as best as you can. The painting is a lot of effort to only get 2 or 3 rides out of, I found it easier to give it the WD40 treatment every ride/wash.
Click on my link in my signature, there are pics of my '00 KX250 with the pipe finished this way.