I just figured out how to get it to work. I created a team and it worked fine.
Go here:
http://fantasygames.sportingnews.com/baseball/stratomatic/2003/your_teams.html
on the left side of the page, click on "fules / faq" in the info section.
Somewhere toward the top of that FAQ in the signing up section is a section labeled free trial teams.
Click on the "create your free trial team here" link.
As of now, there is 1 open spot in the league. Once that fills, a new one will open up in it's place.