you need to do the following. I
First I'm making the assumption that you are using XP home/pro:
What I'm about to tell you, if you choose to do it, will be to modify a registry key. Doing so incorrectly can cause instability in your system, so if something goes wrong, Don't start pointing blame.
ok, first, run regedit. Then browse to HKEY_LOCAL_MACHINE\software\policies\microsoft\win dows
at this level create a new key. name the key "Psched"
open this key. Create a new Dword value named "NonBestEffortLimit" and give it a value 0
This will do what you are reguesting.