reaally slow vista pc

I have a dell pc laptop running windows vista. It is horribly slow in starting up and running applications, the device is a few months old and I haven’t installed any apps but itunes and ms word. I felt like it may have been norton slowing it down but closing the app did not change much. All I know is that my page file usage is normally very high… Can anyone please help me out here on how to keep it from lagging so much??? Thanks!