I know different departments have different standards about drug usage, but I am just looking for a general answer, and I guess some general comfort...
I have previous drug usage from June 2002 (I was 18 and just graduated high school). I fell into a bad crowd briefly and tried various things. Nothing with needles though. However, are there specific drugs that automatically disqualify you from working as an officer? Is there a certain number of drugs that would disqualify you (like more than 2 different ones)? I haven't tried that many but either way, it was once each and I'm nervous about getting hired. Any ideas?

Simply be honest and upfront when they ask you about any prior drug use and the approximate times. Big thing is do not lie. As GTS said, it seems like every dept is different. I hope you have learned just how stupid it was and what poor judgement you had. Learn from it. The better officers I have known are often the ones that could have gone either way at one time.