Also, check this page out - it demonstrates bidirectional ExternalInterface() communication inside a form in IE and includes the FLA!
And don't remember how you got here: Steve Kamerman's Blog
You should be able to select a day / time / duration from the calendar and Flash will run this command:
ExternalInterface.call("getDateRangeFromChooser", [startDate,endDate,start_element,end_element])
...that will call the Javescript function "getDateRangeFromChooser()" and pass an array of four arguments to it, which in turn will set the two text boxes to the start date chosen and the calculated end date.
This code is not licensed for public distribution and is property of Tera Technologies, Inc. It is displayed here for reference sake only!
Please direct questions to kamermans@teratechnologies.net