I think the code bandi posted does just that - it may appear to be not so because the result window probably is using a proportional font.
If you know how far to the right you want the asterisk to be, another way would be to cast it to char or nchar of that length and then append the star. For example:SELECT CAST(LEFT(col,LEN(col)-1) AS CHAR(40))+'*'
FROM @t