touchpad pointer acts crazy

Hi! to all,
I have a PC with xp home and a dial-up connection from my ISP. I run ZoneAlarm for a firewall. I have up dated my touchpad drivers from Dell. I have noticed that at start-up, my touchpad point acts crazy (either jumps all over or will not move) this seems to take place when the Avast (home /free) scanning is taking place (if I turn it off, this stops). Any ideas as to why this is happening? I have tried different touchpad pointer options (in the control panel).
Thanks.