This is with Vista SP1 installed. I added 2GB RAM making the total
installed RAM size to be 4GB.
My problem is that although BIOS recognize the RAM size to be 4GB and
the Properties/System shows also 4GB, but both of the System
Information/System Tools and Performance/Task Manager show 2GB.

How can I check to see if 4GB is being made available for the system to
utilize?