Unfortunately it is a little bit tricky to get the default welcome file index.do working with Struts and Jetty. Suppose you have th following web.xml:

...
<welcome-file-list>
  <welcome-file>index.do</welcome-file>
</welcome-file-list>
...

and you have configured the ActionServlet to listen on *.do requests. Then you would assume that

http://some.url.com/index.do

would work? Right? No! I guess the problem is that the default servlet (which handles the welcome-file stuff) looks for the file index.do on the filesystem. Unless there is no such file the ActionSerlvet will never be called.
The trick is to simply add an empty index.do file in the root directory of your WAR. That's it =)