Internet Providers have a specific block of IP addresses. They assign one of these to each customer at login. When you hang up the IP is reused for another login. They are traceable. Your IP usually will stay the same as long as you stay connected but some providers change your assigned IP on a random basis even when you do not log off. They do this to discourage users from running an FTP server and taking up a lot of bandwidth. Even though most users are under the impression that they should get the bandwidth they thought they are paying for, the providers limit your throughput.
There are many sites that provide lookup service for IP addresses. Such as:
http://www.webyield.net/domainquery.html
http://www.ipaddressreport.com/
They show who owns the IP block but it can be very misleading.
From an IP you can find the company and general area of the IP block OWNER. That may not be the area where the post was made. I am in Florida but the IP block is owned by Bank Of America in California. The provider can tell exactly what computer was assigned to any of their IP’s at any time. As far as I know the providers are required to keep records of this information so the government can track criminals.
The odds against two or three users on this site getting the same IP on the same day is very very low. Unless this message base is doing something funky with the IP’s it shows on the posts, there is in my opinion, one computer or network posting as different users. There are ways around this but it is cost prohibitive just to start BS on a fishing board, unless you have access to the raw data and edit that data.
Larry