The solution to stop MTB disc brake squeaking?

I've asked about half a dozen questions about this subject, and I've tried what people have suggested to do about my disc brake squeaking when I stop, but nothing has helped. I have tried lightly sanding the pads and the disc, and I have tried cleaning the disc with rubbing alcohol. What I would do is clean the disc with rubbing alcohol first, then sand the disc, then clean it again with rubbing alcohol so that no metal particles would be left lying around. I actually did this yesterday (6-26-09). The shrieking did stop, but after a few stops, it came back again. I suspect that the front of the pads aren't touching the disc first, but I don't know how to fix that. Is there something I didn't do to help resolve the agitating squeaking of my disc brakes? Please try to keep answers to DIY (Do-It-Yourself) jobs to fix this problem. ALL HELPFUL ANSWERS ARE BEYOND HIGHLY APPRECIATED!