Indexed Sales -HELLLLP

Hi there, having a few difficulties, really hoping some one can help,
I have to present sales Indexed, here are my sales unindexed

APR-JUN 2003 £325,719
JUL-SEPT 2003 £275,230
OCT-DEC 2003 £306,321
JAN-MAR 2004 £396,208

My index as as follows:-

1st Qtr 2002/03 = 231.80
1st Qtr 2003/04 = 239.30
2nd Qtr 2003/04 = 241.50
3rd Qtr 2003/04 = 244.00
4th Qtr 2003/04 = 241.80

How do I obtain my Indexed sales for periods:-
APR-JUN 2003
JUL-SEPT 2003
OCT-DEC 2003
JAN-MAR 2004

If some one could explain in simple terms what "indexed" means and how to calculate it would really be appreciated !!!

Many thanks in advance FF