Besides the physical number of slots for RAM, here are the Windows limitations.  As you will see the Windows answer for more memory is ’64 bit’. 

Some key points here:

• For Windows XP / Vista 32 bit have at least 2GB but try for 4GB
• 32 bit Windows (XP or Vista or 7) can only address 4GB of RAM, anything more is completely unused.
  (It really ends up being between 3.0GB and 3.5GB since 512MB is lost due to PCI Architecture and 256MB is lost for the Video Card (or whatever memory the card has).
• 64 bit Vista can only be installed on a 64 bit machine.
• 32 bit Vista / XP can be installed on a 32 bit or a 64 bit machine.
• In the 64 bit OS, 64 bit drivers must be signed and 32 bit drivers are not supported.
• Programs must be written for 64 bit in order to take advantage of these features.

Office 2007 is still a 32 bit program but almost all features will work on a 64 bit OS.

Windows Vista Compatibility Center
http://www.microsoft.com/windows/compatibility

To check for 64 bit software compatibility

-          Click the ‘software’ tab

-          Then after finding software make sure the system type (along the left) is ’64-bit Windows Vista’

Memory Limits for Windows Releases

http://msdn.microsoft.com/en-us/library/aa366778.aspx

Physical Memory Limits: Windows XP

The following table specifies the limits on physical memory for Windows XP.

Physical Memory Limits: Windows Vista

The following table specifies the limits on physical memory for Windows Vista.

Memory and Address Space Limits

Access 'Local Only'

Instead of

Access ‘Local and Internet’

In the Network and Sharing Center

And you can’t browse the internet (but you can access local devices).

One solution that worked for me:

1.       Control Panel -> Network and Sharing Center -> Manage network connections

2.       Get properties for the wireless adapter

3.       Uncheck IPV6.

This is how it should look: