Can you do the following.
in cell a1 put 0
in cell a2 put =a1+1
drag this down untilyou get to 99999999
in cell1 put =text(a1,"00000000")
drag this formula down
you should have a list of 8 digits of all possible combinations.
On excel 2003 you will only have 65k rows so you'll have to split them up over multiple columns.
for i = 0 to 99999999
'your code goes here
'maybe something like:
'format(i,"00000000")
next i