By toning down some of the fancy display options (shadows, textures, highlights), you can speed up system performance. As with many other speed tweaks, how much it helps, varies.
Click Start->control panel->system settings->advanced->settings
Simply Select 'Adjust for best performance'
Click Start->Control Panel->Appearance and Personalization->Personalization
Choose Windows Classic theme
Tip: Using a plain solid color desktop may improve performance.