I'm very proud to announce AltCal, an Excel spreadsheet to build julian or
gregorian calendars from 4713 BC to ... 1465001 AD (!) freely downloadable
at <
http://www.ensemble-fr.com/~scaliger/>.
Don't miss it. It's really free, and there are some pieces of Visual Basic
to compute julian and gregorian to julian day number and the date of easter
(in both calendars).
I hope you'll enjoy it.