Until now "Lock Pages In Memory" was an option only available to SQL Server Enterprise Edition customers. Very simply put it prevents SQL Server from paging out the memory it has allocated (a deep explanation can be found in the references below). We got a lot of feedback from customers who wanted to have support for this in SQL Server Standard Edition too. So we are very pleased to announce that it will be available in SQL Server 2005 and SQL Server 2008 Standard Edition too (as of SQL Server 2005 SP3 CU4 and SQL Server 2008 SP1 CU2). As with everything do not just enable this option by default but carefully plan and test.
More information on this can be found on http://blogs.msdn.com/psssql/archive/2009/04/24/sql-server-locked-pages-and-standard-sku.aspx
Slava Oks did a great job in explaining the Lock Pages In Memory (and AWE) mechanism on http://blogs.msdn.com/slavao/archive/2005/04/29/413425.aspx and http://blogs.msdn.com/slavao/archive/2005/08/31/458545.aspx.