Indexes with few values

Suppose I have a table where one of the columns has only three different values :

null 1 miljon rows
'J' 1 miljon rows
'N' 0 - 100 rows.

If I want to search for rows with the value 'N' then an index would help wouldn't it ?

TIA Mats

Mats Larsson          |  Tel:   +46 8 7647921 
                      |  Fax:   +46 8 6279632
171 94 Solna, Sweden  |  Email: matlar_at_rsv.se