You need AWE to prevent memory stealing by the OS.

Also make sure you have a minimum and maximum size. Don't set the maximum size to unlimited, or SQL will compete with your OS for the last MBs.

We have the same configuration and our max memorysize is 28GB (min size is 16GB)

Also, be aware of memory trashing if you do a large OS filecopy on that server.

You also get memory messages in your logfile when adding/deleting databases/snapshots, but these are ok.