One reason to switch to 64-bit SQL Server.
The 32-bit platform
The 32-bit platform (x86) has the least amount of buffer cache. Buffer cache cannot reside within the Address Windowing Extension (AWE)-controlled memory space; it has to be in the first 2 Gigs of RAM allocated to the SQL Server instance. On the 32-bit platform SQL Server 2000 and SQL Server 2005, both use the same base calculation to find the amount of procedure cache to use. SQL Server will use up to 1 GB of memory, or 50% of the memory, whichever is lower.