With your first statement, is ISP used for tracking?
I believe that, which is a common mistake, you are mixing up IP and ISP. Your IP is basically a phone number, but for your computer, people can track you using it and see what connections are coming from where and when.
Internet forums often use IPs to find spammers, so they can use a sort of 'global' ban on that IP, keeping them from being able to create new accounts or access the site from the said IP. The same thing can sometimes be done with e-mails, and other services but IPs are often hidden except to administrators.
Your ISP is essentially who you pay to give you this wonderful tool called the internet, Internet Service Provider.
Common ones are Comcast, Roadrunner, Qwest.
Some websites that can further define for you:
http://en.wikipedia.org/wiki/ISP
http://en.wikipedia.org/wiki/IP_address
BTW, my phone metaphor may have been a bad one, it's just what I had on the tips of my fingers =)