they are strings.
Which way you go depends on whether you need them stored with the leading zeros.
If you can get away with just displaying like that, and you need to do math or data entry validation. Then a display format will work.
If Mr wills idea of using display format doesn't suit.
The sql way of turning 15489 into '00015489' is
Select Replicate('0',8 - DataLength(Convert(VarChar(8),15489))) + Convert(VarChar(8),15489)
You could also do it with the VB style functions such as Length, and CStr, though if you ever choose to use a full DBMS, they will cause you problems
HtHs