If it was Friday on March 9, 2007, which day was it on March 9, 2003?

 Sunday

Total number of odd days between the years 2003 and 2007 = (2007 - 2003) + 1 = 5 odd days.

The year 2004 is a leap year, it has two odd days.

So, one extra odd day is added. So, if it was Wednesday on March 1, 2007, it would be ( Friday - 5)  = Sunday on March 9, 2003.