How much RAM I should assign to SQL Server 2008 running on W2K3 I'm planning an installation for SQL 2008 over Windows 2003.  The server has 16g RAM. How much RAM I should assign to SQL server?
12GB, leave 4GB for the OS.

This 12GB is for the various caches. The binaries and various out-of-process calls will use the 4GB, along with the OS.