I'll save you the trouble.<g>

If there is only one leading letter character for each "field" in the cell
and if the number part always needs to be three digits long, then this sub
should work...

Sub AddZeroes()
 Dim C As Range
 Dim Fields() As String
 For Each C In Selection
   Fields = Split(C.Value, ",")
   For X = 0 To UBound(Fields)
     Fields(X) = Left$(Fields(X), 1) & _
                 Format$(Mid$(Fields(X), 2), "000")
   Next
   C.Value = Join(Fields, ",")
 Next
End Sub

To ENFGDC4S:
=============
All you have to do is right-click the sheet tab at the bottom, and "View
Code"; then copy/paste the above routine into the sheet's code window. Once
you have done that, go back to the spreadsheet and select the cells you want
to apply this routine to and then press Alt+F8 and run the AddZeroes macro
from the dialog box that appears.

Rick

The alpha character will be a single character and followed by up to 3
numerals.
There is a posibility of up to 4 numerals but does not happen much. 3
numerals will be fine
I would only need the leading zeros if the numeral is from 1 - 99, for
example,
C3,C34 would be C003,C034.
There is also a comma after each item.
These are Reference Designators on a printed wiring board and are used in
the parts list for idenification.