Re: Question on amount of RAM

You can verify that the OS is presented all 4GB by checking system information. Programs>Accessories>System Tools>System Information. It should list the full 4GB there.

You can research Physical Address Extension to possibly enable more memory. It is available in XP service pack 2 and later. It may allow you to use more of the memory if enabled. If you don't have access to this page on MSDN then you should be able to find alternatives with a search:

http://msdn.microsoft.com/en-us/library/windows/hardware/gg487503.aspx

Thanks