Auto Processor affinity

Hello, is there any program out there that will automatically set a programs affinity to work on a single processor? I have a quad core system and would usually divide my cores up, but it's a nuisance having to set it manually everytime that i have to encode or watch an HD recording. I'm running Win 7 and if theres anything for Vista out there hopefully it should be stable in 7.

 

Here's a good guide
http://www.vistax64.com/gaming/197915-setting-processor-affinity-made-easy.html

 

Seems to work but also slower than if I manually did it lol thank you though