SQLServerPedia

SQL Server’s memory limits are determined both by the Operating System limits and by the Edition of SQL Server. You should read the following articles to understand the differences between SQL Server 2000 [Edition] Features and SQL Server 2005 [Edition] Features. Then, you can move on to Server Memory Options and How to configure SQL Server to use more than 2 GB of physical memory.

To see how much memory your SQL Server is consuming, you can use Performance Monitor, specifically looking at the SQL Server: Memory Manager: Total Server Memory (KB) counter, among others. A full article is available on MSDN called Monitoring Memory Usage.

Hope that helps.