You want to enable the 3GB switch on the Windows Vista™ or Windows 7 operating systems.

To enable the 3GB switch on Windows Vista™ or Windows 7:

1. Right-click Command Prompt in the Accessories program group of the Start menu. Click Run as Administrator.
2. At the command prompt, enter "bcdedit /set IncreaseUserVa 3072"
3. Restart the computer.

To disable the 3GB switch:

1. Right-click on Command Prompt in the Accessories program group of the Start menu. Click Run as Administrator.
2. At the command prompt, enter "bcdedit /deletevalue IncreaseUserVa"
3. Restart the computer.

For more information on the 3GB switch, refer to the following Microsoft MSDN article:

http://msdn.microsoft.com/en-us/library/ff556232.aspx

Here is the original post from Autodesk:  http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=9583842&linkID=9240617&CMP=OTC-RSSSUP01