For Vista/Windows7 32-bit users:

1.. Click the Start button or press the Windows key
2.. Type *CMD* in the search box, then press the Enter key (If you do not normally have administrative privileges, use Ctrl+Shift+Enter instead of Enter. Type .. and then hit Enter. Repeat this until you see C:\)
3.. Type *bcdedit.exe /set IncreaseUserVa 2600* then press press the Enter key
4.. Restart the computer for the changes to take effect.

To revert this setting back, repeat these steps but instead of /set IncreaseUserVa 2600, type /deletevalue IncreaseUserVa

For XP 32-bit users:

1.. Right-click My Computer and select Properties. The System Properties dialog box will appear.
2.. Click the Advanced tab.
3.. In the Startup and Recovery area, click Settings. The Startup and Recovery dialog box will appear.
4.. In the System startup area, click Edit. This will open the Windows
*boot.ini* file in Notepad.
5.. In the [Operating Systems] section, add the following switch to the end of the startup line that includes /fastdetect: /3GB /USERVA=2600(with a space between /fastdetect and /3GB)
6.. Save the changes and close Notepad.
7.. Click OK two times to close the open dialog boxes, and then restart the computer for the change to take effect.

Edit Note: Adjusted the process space to go up to 2.6GB instead, for stability and avoid conflict with video drivers with large vram.

Source Forum officiel.