Excel 2007 : Removing Duplicates - But Only Some

Hi All,
Ok, so got a tricky one.

remvoing duplicates is easy i know in 2007. However, I only need to remove some of the duplicates.

So for example, in column A there is an ID number, which can either be one unique code, or 5 lines of unique code. In Column B it has a folder number..The folder number is a different number, however matches up to each row.

What is happening is that there are duplicates and we need to find out what duplicates there are.
Sometimes there is 2 rows of the same code in column A, however 2 different folder numbers in column B. We need to possibly create an extra column and put a mark of some sort in a different column so we can do a sort or a count later one.

But, if there is 6 rows of the same code in column A, and 2 numbers in Column B, we need to keep say the first 3 codes and the first set of numbers and mark the other 3.

Basically each line of code is a page, and to charge properly we need to know how many numbers.

Let me know if I have confused you or if you can help

Thanks

In the below example, only rows 3, 5 and 7 would be highlighted or say an asterix in column C..

Column A Column B
123456 2
123456 3
1234567 4
1234567 5
12345678 6
12345678 6
12345678 7
12345678 7