XP Home cursor freezes, OS locks, has to hard reboot

Im running XP Home on an AMD Athlon 1700 with a GeForce 2 vid card and (1) GB of PC2100 RAM. In the last 6 months, the cursor started to freeze (not respond to mouse movement) and I had no keyboard or mouse control over XP. I have to hard reboot to regain control of the mouse and keyboard in XP. In addition, any downloads from the web stop as well. In short, the entire XP becomes inaccessible. I use Zone Alarm for my DSL connection and it too STOPS and shows no activity. Ive upgraded and downgraded the video driver several times, Ive reformmated and reinstalled XP several times, and yet the problem persists. My experience tells me its a driver conflict problem but the system will ON ITS OWN freeze just in the process of a download when Im in the other room doing something else. Does anyone have any idea what this behavior might be caused by? I cant even access the Dr Watson log file because after the hard reboot, that file data is lost. HELP! Please. Thank you.