Not sure if this will help, but one method I realized was possible
this morning that handles dates and was "staring me in the face", is
to do "bulk entry" of tasks through the Rapid Task dialog. You can
just paste in an item or list of items like this:
Item one 02/20/11
Item two 02/21/11
Item three 03/15/11
And with parsing and multiple entry turned on, it will enter the items
at the place you choose in the outline and add the dates to the due
date field. If you look in the Application help for Input parsing, it
will show ways to designate start date, due date etc in the text
string.
I chose this method rather than trying to come up with an xml
solution.
Hope that may be helpful for you.