In Eclipse I have set the Javadoc Location property of my Scala project to file:/D:/EclipseWorkspace/MyProject/target/scala-2.9.1/api
Scaladoc is now integrated since release 4.0.0 RC1 of the Scala-IDE plugin. You can just hover over your term, or press F2 while the cursor is on the identifier.
Typesafe has announced a plugin for the Scala compiler which generates JavaDoc for your Scala API. The plugin and its documentation is available on github. Maybe this helps as a workaround.