Why don't you talk to Hans-Juergen Heinrichs to use these and be done with it:
http://www.avrfreaks.net/index.php?module=Freaks%20Academy&func=viewItem&item_id=665&item_type=project
Unlike the standard AVR libC <util/delay.h> routines, these give you very accurate timings with good resolution even in the sub microsecond range.
--- bill