This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Yes, applets can be delivered as jar files. In fact, that's the most common method in which they are deployed. But applets do not use a class having a "main" method like applications do, so they have no Main-Class attribute in the manifest.
To run the applet you'll need an HTML file that contains an <applet> tag, which is described in detail on this page of the Java Tutorial.