coolhandbert,
The browser appears to be showing only classes, not interfaces. I’ve raised a problem report for this. However, setting the type manually should work as the browser is just an assist. Also, if you enter “Datasource” in the Res-Type entry field (either in the web.xml editor or in the first dialog that comes up when you hit the Browse button) and then use content assist (Ctrl-Space), you will see javax.sql.Datasource in the list there.
What is the deployment problem that you are getting when you enter the resource type yourself? Please provide as much information as you can, including the steps to see the problem, any associated log messages, your OS and the target server.