Web seminars are, by most definitions of project management, projects.  Unlike ‘normal work,’ projects (and web seminars) bear three distinct characteristics.

Finite duration
Web seminars, like projects, have starting and ending points.  The end point, of course, is the event itself.  Projects are not ongoing, recurring work (e.g. ‘get the TPS report out every week).  Web seminars may get strung together into campaigns, but I’d still argue that that’s one big project made of several little ones.  The goal is to end it all…successfully.

Goal-oriented
Projects have stated objectives, and web seminars should also.  And don’t say ‘to get the word out.’  You’ll get shot by some disgruntled, unemployed marketer looking to get a real job by decreasing the labor supply.  A key characteristic of projects is that they can be broken down into tasks that can be sequenced from ‘Point A’ to ‘Point B.’

Unique/non-routine
If you do it all the time, it’s probably not a project, it’s a job description.  Web seminars typically have unique problems or situations, unique people and messages. 

Web seminars are projects.  Learn project management.