I haven't read all 4 pages of this thread, so excuse me if this has already been suggested/answered.
Are you using AOL as your Internet Service Provider? If you are then you should be aware that AOL caches everything on your website to different servers, resulting in multiple entries for the same page visited - up to 20 or more per page. This traditionally shows up in your web stats programme as multiple entries from different ip addresses, all at the same time (the different ip addresses being the different servers being cached on).
However, I suppose it's also possible that by using AOL to access your site the Who's Online feature may show multiple entries from the same broadband/dial-up ip address.
This problem can also occur if you have a corrupted session id stored in the database, which can be cured by accessing the db via phpMyAdmin, clicking on the 'sessions' table link in the left column and then electing to "Empty" or "Truncate" the sessions table (removing all stored sessions). Just make sure that you don't elect to "Drop" the table or else you'll have to recreate it completely.
Vger