Here is a post sketching a procedure for consolidating to a single zip, from which you could read the xml more simply:

http://forums.omnigroup.com/showpost...1&postcount=13

(I have to say that in the end I have retreated from processing the zips directly a couple of times, and settled for the simplicity of getting property value lists from Applescript):

tell front document

set refFlagged to a reference to (flattened tasks where (flagged is true) and (completed is false))
set {lstName, lstNote, lstDue, lstDurn} to {name, note, due date, estimated minutes} of refFlagged

end tell

Getting something like cron to run an applescript from the shell with osascript, perhaps ?

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