How to configure AWE memory

AWE according to BOL:
SQL Server 2005 Enterprise Edition supports Address Windowing Extensions (AWE) allowing use of physical memory over 4 gigabytes (GB) on 32-bit versions of Microsoft Windows operating systems. Up to 64 GB of physical memory is supported.

My advice: Don't use AWE!
As mentioned above, it is only supported by the far more expensive SQL Server Enterprise edition (32bit of course) and it is only used by the core database engine and no other components.
SSIS -and others- won't benefit and are still limited to 32bit (=2GB max).
AWE has also a performance overhead, and it's always a hassle with the boot.ini switches:

If your system has <= 4 GB - use /3GB (none of the other options)
If your system has > 4 GB and < 16 GB - use /3GB and /PAE and configure AWE in SSMS
If your system has > 16 GB - use /PAE and configure AWE in SSMS

Go for SQL Server standard Edition (which is more then enough for most shops) and go for a 64bit environment with enough memory (start with 8GB) for SQL Server to use.
Far Cheaper and far more scalable.
You can serve more databases on the same instance, leading to substantial cost savings.

See my post on Tools for performance and How many instances on a SQL Server