Well, I know that wires when they have current flowing through them (ie, attached to PSP etc and PC is switched on) cause a magnetic field around them which can cause interference, but I've never seen anything of the magnitude.
You may want to invest in a new mouse (I never ever trusted Packard Hell), it's possible its just sensitive, but if it was expensive, just keep the wires away
.
Btw, I just remembered something else - the phone itself will cause interference, but you don't mention it being there or you moving it or such
. (if you want an example of this, place it next to a speaker and phone it from a landline).