Something like this - Be Careful!!!! This would delete all of the todos from iCal.
Code:
tell application "iCal"
set theCalendars to every calendar
repeat with theCalendar in theCalendars
set theTodos to every todo in theCalendar
repeat with theTodo in theTodos
set theTodoSummary to summary of theTodo
tell application "OmniFocus" to tell default document
make new inbox task with properties {name:theTodoSummary}
end tell
delete theTodo
end repeat
end repeat
end tell
Chris