Read this article by Microsoft: http://support.microsoft.com/kb/308417
especially this part:Manually manage processor scheduling
There are a finite number of resources that are available for a computer's CPU. Windows manages these resources automatically, and can allocate tasks between processors or manage multiple processes on a single processor. You can adjust how Windows manages these resources by prioritizing them between the foreground programs and the background services.
By default, Windows puts a priority on the foreground programs. The added processing resources cause programs to respond more quickly. However, if you have background services, such as printing or disk backup that run while you work and you want them to respond faster, you can have Windows share processor resources equally between background and foreground programs.Note: My personal recommendation is to allocate more resources to background services.
To manually change the performance of foreground and background programs, complete these steps:
1. Click Start, click Run, type sysdm.cpl in the Open box, and then press ENTER to open the System Properties dialog box.
2. Click the Advanced tab, and then under Performance click Settings.
3. Click the Advanced tab, and then under Processor scheduling use one of the following methods:
* Click Programs to assign more processor resources to the foreground programs. This setting is recommended for most users.
* Click Background services to assign equal amounts of processor resources to all running services. This includes print jobs and applications.
4. Click OK to apply preferences and close the dialog box.