Count A Number Of Times A String Appears but display the number sequence

Hi, I'm using excel 2000 and I need to get around this problem I'm having any help would be great.

So for example I have a column of string data

A
A
A
B
A
B
B

I need to know the number of occurrences of the letters, I know I can use COUNTIF to get the total but I need the number sequence to be displayed like this

A 1
A 2
A 3
B 1
A 4
B 2
B 3

As calculations need to be performed at each instance, any ideas? Anyone??