Wasn't sure about the input format, especially the "-Mon-" segment. Maybe...

DECLARE @Dob TABLE (birth VARCHAR(15))

INSERT INTO @Dob

SELECT '24-Oct-2012'

UNION ALL

SELECT '01-Jan-2011'

SELECT birth AS 'Input'

, CONVERT(VARCHAR(15), CAST(birth AS DATETIME), 103) AS 'Converted'

FROM @Dob

Input Converted

24-Oct-201224/10/2012

01-Jan-201101/01/2011

(But of course you know you should never store dates as strings, right?)