Update a table with an incremental number for each occurrence of a value

[John Galvin]

Hi There,

Ideally I am looking for a way to append a numerical value to each record where it has found a recurrence of a value, e.g. where the data captured is firstname, lastname, email, item and price:

John, Galvin, [e-mail], Camera, 200.00
John, Galvin, [e-mail], Tripod, 34.99
John, Galvin, [e-mail], Memory Stick, 65.00
Tony, Galvin, [e-mail], Phone, 150.00
Tony, Galvin, [e-mail], Phone Case, 25.00
Bill, Galvin, [e-mail], MP3 Player, 70.00

The field which we're using to count on is email address, and ideally the result I would like is to append a numerical value which corresponds to the number of distinct orders for that email address:

John, Galvin, [e-mail], Camera, 200.00, 1
John, Galvin, [e-mail], Tripod, 34.99, 2
John, Galvin, [e-mail], Memory Stick, 65.00, 3
Tony, Galvin, [e-mail], Phone, 150.00, 1
Tony, Galvin, [e-mail], Phone Case, 25.00, 2
Bill, Galvin, [e-mail], MP3 Player, 70.00, 1

Can anybody suggest a way of achieving this?

Thanks

John