There've been a lot of answers to this question and they could all be unnecessary because SQL Server is very forgiving for most date formats. With that thought in mind, what does the original data look like? And I'm not just talking about the month name. For example, if your trying to convert a string to an SQL Datetime and the date looks like '1 June 2010', there you don't need to find the month number to do the conversion....

SELECT CAST('4 June 2010' AS DATETIME)