As far as I know the bumper-to-bumper warranty is 3/36k. Maybe they changed it for the '02 models (highly unlikely), but that's what I understand from the '01. I can check my warranty booklet, but you could check yours too....
Anyhow, to answer your original question:
Dropping the car and adding an A/V system won't exactly void your warranty, but it could void your warranty for certain parts of the car. For instance, if the electrical system malfunctions as a result of your system, then the dealer could be very reluctant to service the electrical system under warranty. Also for the lowering thing, if you tear up your emissions system as a result of scraping speed bumps, they may not want to honor the warranty on emissions sytems. Of course if you redo the suspension and add an A/V system and your transmission explodes.....then they'd honor the warranty on the transmission. Beware the exploding transmission.
For warranty work, though, it basically boils down to a couple points.
1. First decision to honor warranty is up to the dealer, some are real cool, some aren't that cool. You can always dispute the warranty claim with the regional office if you'd like, or just try another dealer. More info on that is in your warranty booklet that came with the car.
2. Legally speaking, the dealer must be able to prove that YOUR change to the car specifically caused the failure in order to NOT honor the warranty. This can be rather tough to do depending on what the warranty claim is about.
My general experience with Honda dealers is that they're usually good about honoring warranty work (unlike VW).