calculate interest between dates

i like to know that how to calculat amount of interest between two dates in a exel worksheet when rate of interest varies with financial year i:e
from 1/4/2000 to 31/3/2001 rate is 10%
from 1/4/2001 to 31/3/2002 rate is 10%
from 1/4/2002 to 31/3/2003 rate is 10%
from 1/4/2003 to 31/3/2004 rate is 10%
from 1/4/2004 to 31/3/2005 rate is 10%
from 1/4/2005 to 31/3/2006 rate is 10%
i want to enter start date i;e 21/6/2000 & last date i;e 23/6/2005 & the amount 100 rest need formula to do.