It is possible. There are some guys at software.softeu.cz who host a maven 2 repository of seam and related dependencies. If you build a maven 2 project using one of their archetypes, http://software.softeu.cz/archetypes/, then they provide a jetty target which will build your project, start jetty, and deploy your project to it. You just type "mvn jetty:run".
So, you could either start a new project using one of their archetypes, or you could do up a sample project, run the mvn jetty:run command, and examine the generated output, and then apply that back to your own project.
Thanks, I'll check it out. Maybe for learning Seam (it's all pretty new to me) it is better to stick to JBoss AS at first though.
Using the archtypes mentioned above, there are still problems incorporating EJB3 with jetty, it seems it's still on the TODO list.