Mouse Problems

My mouse seems to have developed a stability problem, I’m running Windows 2000, when I open an application such as word or other GUI type prog. the mouse gets very Jittery – unresponsive to movement &/or mouse clicks.
I’ve tried reloading the driver, I haven’t loaded any new programs. first noticed problem when downloading with Grokster – now seems to be more frequent. (the mouse is a Logitech cordless – I’ve cleaned the ball & rollers & made sure there are no other radio / magnetic devices causing interferance).

Thanks in advance.