The first day of spring is March 20 or 21, and both the date and the day of the week variy from year to year. Spring will start on Saturday March 20 in 2010.
The first day of the week is Sunday.
It depends where you live -- in the USA, Sunday is typically the first day on the calendars, but in the rest of the world it's mostly Monday.
Saturday
March 20
If you are a Christian, then the first day of the earth was Monday