BUG: Not all memory is available when AWE is enabled on a computer that is running a 32-bit version of SQL Server 2000 SP4
Alas SQL Server 2000 SP4 has introduced a bug that prevents all one's memory being used if you are using AWE - please see the following article.
https://support.microsoft.com/default.aspx?scid=kb;en-us;899761
Microsoft will post a fix for this once testing is complete, as soon as I see it I will blog it. However if this bug is a real problem (you can't rollback) contact Product Support and they will help you with a solution. For this issue your support call should be free.