Here are steps to increase or decrease the priority of any process on Windows XP/2000 machine!

1. Press CTRL+SHIFT+ESC or CTRL+ALT+DEL
2. Go to the second tab called Processes, right click on one of the active processes, you will see the Set Priority option. (as shown in following screenshot.)
3. Default is normal, change it to…
   • AboveNormal, High, Realtime to increase process priority OR
   • BelowNormal, Low to decrease process priority!

FAQ:
Q. Why I need this?
Ans: When multiple programs are running, there may be few dear programs. Like some anti-virus scanning is running along with some movie, you will get smooth decoding of movie by increasing its process priority and/or decreasing process priority of antivirus.

Note: If only a single program is running then it may not get benefit from changing priority!