Application is running really slow

I am trying to covert the resolution of the video from 640x320 to 1020x720 but the program I am using is taking to long. Its only using like 8.3 cpu when running. (Xilisoft Video Converter) Does any one know a better/faster application to do this with or a way to up/control the cpu usage. I know there is a program called cpu speed accelerator but I have not tried it. Is any one familiar with this program, whether or not it is any good. I would really like to find a good program that allows you to have control over the cpu usage. THANKS