SQL Server uses more memory than maximum setting
To contribute a little more to this, there is a post on dba.stackexchange.com that explains this situation a little more: SQL Server Max Memory not limiting use of RAM.  Also, in the answers on that question, Mark Storey-Smith recommends reading Brent Ozar's article "A Sysadmin's Guide to Microsoft SQL Server Memory" to further one's understanding on how Microsoft SQL Server handles memory.  I second that recommendation.