I'm on a cable modem and I wonder if my personal IP (I have been told that the number changes) can be tracked and if I can be located by "people" who might not be happy with what i'm doing.

There are two categories of "bad" people:

1) Crackers who may want to break into your computer

and

2) The RIAA and/or copyright agents who may be concerned about violations

Let's address the people in category #2 first. If such people wanted to, they could log into the gnutella network with a client and start logging the IP address of other clients which are making possible copyrighted material available. They would then, most likely, have to download the material to show that the file title is indeed the copyrighted material for each client (Just because I have available a file called "Like a Virgin.mp3" doesn't mean that the file is indeed that song. It may be my uncle snoring in his sleep).

If these people wanted to they could then easily contact the ISP's providing the service and determine who was using what IP address at what time (ISP's keeps logs of these things). They could then take those people to court and sue for copyright violation damages.

It may be a future part of the strategy of the RIAA to do that to a few people in order to "scare" people from using gnutella. The downside for the RIAA is that they are then suing there customers and a consumer backlash may be very damaging to them. Additionally, the idea of "scaring" people by making examples of a widespread lawbreaking practices is always unsuccessful; witness the numbers of cars speeding on the highways.

Since there are so many people sharing on gnutella, the chances of the RIAA singling out you is low (but not zero). Interestingly enough, the RIAA could have brought legal action against the users of Napster (the files that one gets "from" Napster actual come off the hard drives of Napster users who share files. This is a copyright violation.) , but have so far (wisely) choosen not to antagonize their customers (us!)

The people in category #1 (crackers) are dangerous to a cable modem users even without ever using a gnutella client. Get yourself one of the personal firewires available to prevent someone from breaking into your computer.