Mouse: Left click = doubleclick

One of our workstations has a microsoft wheel ps/2 mouse that automatically double clicks whenever the user left clicks. It makes things pretty tricky for the user. I’ve checked the configuration in control panel. I’ve checked the system properties to see if there is a different driver. I’ve tried switching to other mice. No luck. Is there some Setting in Win98 SE that makes that the default? What should I check?