how can I determine the first day in the calendar

[BushraSQU]

Hi

I want to know how I can make function that determine the first day
in the calendar (Hint: 1/1/1500 is Monday)

[helios]

http://en.wikipedia.org/wiki/Calculating_the_day_of_the_week

[Athar]

http://en.wikipedia.org/wiki/Calculating_the_day_of_the_week

Edit: what to say...