Formula for a date's week number in a month (1st, 2nd, etc.)

i.e. If today is 3/10/06, it falls in the 2nd week of March. Is there a way
to calculate this in a formula? (Also, will there a be a problem where a
date like 3/1/06 falls under the week 5 of February as wells as week 1 of
March?)