Setting priority of a different user which app is running on your user

[mystvearn]

I am opening the same software more than 1 user, but the app only runs on one XP user profile. What I did was I made new XP profiles, and use the "run as" command and put in the other user so that the app can work in more than one copy. My problem is I want to set the priority from normal to below normal for the application. I can do it with the current software which is on the same user machine, but when I open the second software on my current xp profile, I could not change the priority as it says the command is denied. I think its because I placed a Pass protect on the other user as in order for me to run the application successfully on my user, I need to make a password user profile.
Is there any way for me to change the priority of the software? I tried switching profiles but I don't see the software running on the profile and by switching user profiles will cause my net connection to get disconnected. Hope I made it clear. Thanks