I found a particularly interesting comment on the Technet Script Center page for Scheduled Tasks:

Note that this class can only return jobs that are created using either a script or AT.exe. It cannot return information about jobs that are either created by or modified by the Scheduled Task wizard.

A search of the .Net Framework turned up empty. As far as I can tell, schtasks.exe is the way to go if you want the end-users to be able to change the default entry…

UPDATED June 14, 2007:   I used the Task Scheduler library from Code Project.