Use a bit of caution, this may affect other views and stored procedures that use this column. They may, for instance, be using a substring function to get the month string, then use this string in a weird way elsewhere. Another thing you can do is just add a the datetime version of this column to the table. You still have to watch out for inserts that dont spell out the columns being inserted into and select *'s in code elsewhere.

For illustration : This works only when the variable is declared as varchar >

declare @d datetime --varchar(30)

set @d='2012-03-02'

Select (substring(@d,6,2))+'/'+(substring(@d,1,4))