Typically, I recommend creating the permissions with the stored proc and then whatever change control mechanism you use, stored procedure and permissions are stored together to be run together. Eliminates a lot of error.
K. Brian Kelley
http://www.truthsolutions.com/
Author: Start to Finish Guide to SQL Server Performance Monitoring
http://www.netimpress.com/shop/product.asp?ProductID=NI-SQL1
K. Brian Kelley
@kbriankelley