I don't know if I'm running as an Ant task or a builder. Here's what I'm doing ...
From Package Explorer view, right clicking on my build file, select "Run As" and then selecting "Ant Build".
Then I went to Window -> Preferences, and selected Ant -> Runtime, but I can't find the options you reference in there either ...
http://screencast.com/t/Vn93Bo0Gq
Any follow-up advice is much appreciated, - Dave