>>[...]can I set this option programmatically ?
Yes, you can. You just need to issue a call to SetPriorityClass Windows API function. Take a look at
http://www.news2news.com/vfp/?group=-1&function=350 for information on how to do this. The MSDN documentation for this function is also very good and you can get to it from within this URL that I indicated above.
Hector Correa