janus, your question has a few different points to address:
What color are you using? I'd imagine it's aluminum, which should buff out nicely to a good shine, but if you're using some other color, that may be the start of your difficulty.
If you're buffing through the color coat, you're applying too much pressure and/or you haven't sprayed enough coats of paint. You'll want to give a nice primer coat to the pieces prior to applying the metalizer (thoroughly wash and dry the pieces first). Spray the metalizer in a few thin coats until you achieve a uniform coverage, then give it another coat, slightly "wetter" this time. After it's completely dried, gently buff the finish with the softest cloth you have. I use polishing cloth (the fabric stuff, not the grit cloth) or square scraps of cotton t-shirts which have been through the washer over and over to soften 'em up. The trick seems to be to not really apply any pressure. Simply glide the cloth over the paint in a circular motion with just the weight of the material against the finish. You're not rubbing out the paint like you would when polishing it, you're only removing the paint dust and "fly" from the surface.
After buffing it, spray a coat of Metalizer Sealer over it. this will give a protective layer over the metalizer and add a bit of gloss to the finish. If you still want a shinier look, spray it with Future in the usual way.
I've love the metalizer paints. They're not all that hard to use once you get used to 'em, and the results are fantastic. With a bit of practice and luck, buffed aluminum with a clear gloss coat can almost resemble chrome for its shine.
Glenn