IMPORTANT -- We highly recommend not setting the process priority any higher than "AboveNormal."

1. Run the Command & Conquer 3 Tiberium Wars Demo.
2. Press Alt + Tab to minimize the demo and switch back to Windows.
3. Press Ctrl + Alt + Delete to bring up the security prompt and click on "Task Manager".
4. Select the "Processes" tab and look for DemoGame.dat in the list.
5. Right-click on DemoGame.dat, select "Set Priority", and then select "AboveNormal" from the submenu -- this option is one step up from the default "Normal" setting.
6. Windows will prompt you with a similar warning. Select "Yes".
7. Switch back to the game by clicking on the button in the Windows task bar.
   

Via EA Support Forums