Larry has this nailed; though I can’t work out how to add a task in a resource centric view.
Here’s the detail from the 2007 help.
Automatically add new resources and tasks Automatically adds new resources to the resource pool and assigns them default values whenever you enter a new resource name or new resource initials. Clear this check box if you want Project to alert you whenever a new resource or task is created while making a new assignment. Clearing this check box can protect you from adding misspelled resource names or tasks to your project. This is a local setting saved with the active project. By default, this check box is selected.