How about something like this:

select

CASE PATINDEX( '%[a-Z]%', col1)

 WHEN 0 THEN

     stuff('000',4-len(col1),len(col1),col1)

 ELSE

  stuff('000',4-PATINDEX( '%[a-Z]%', col1)+1,len(col1),col1)

 END

from test1

Where test1 is the table in question and col1 is the column you are working on.