32 or 64 bit SQL Server?

Server 2003 will do this to SQL 2005 quite a bit on some systems, and on others it's not an issue. It depends on what else is running and is difficult to predict which systems might be affected. The issue has mostly disappeared with Server 2008 running SQL 2008, and newer setups.

For your case, enabling 'locked pages in memory' (LPIM) is the way to go and is transparent to existing SQL Server operations. Before enabling LPIM set 'max server memory' very conservatively at first and then monitor the 'available megabytes' perfmon counter closely to ensure Windows always has enough free memory thoughout the normal working cycles (day, week, month, etc.). If Windows suddenly requires more memory, with LPIM enabled SQL Server will not return it on request because its pages are locked. In this scenario you can start seeing overall system stability issues which is far worse than Windows simply trimming SQL Server's working set.