Bluetooth priority for keyboard and mouse

Hello,

I've purchased a wireless bluetooth keyboard and mouse set of microsoft (desktop elite for bluetooth).
In general the set works great, but sometimes when my system is under heavy load, my mouse and keyboard aren't that responsive. I think maybe it's because the bluetooth device isn't prioritized same as a ps2 port is.
I have a relatively high end system (Q6600, 4GB RAM, etc) and there is no reason for this unresponsiveness to occur unless it is really not prioritiezd in windows xp pro.

Someone ever faced this issue ? know what I can do with it ?

Thanks in advance.