Scratch disks?

Hello, I am using Adobe Photoshop 7 and whenever I try to start it, a little box pops up that says, "Cannot initialize Photoshop because the scratch disks are full." What are the scratch disks, and how can I empty them, if they are able to be emptied? Is there a way I can solve this problem? Please help me. I want to make some icons and I only use my Paint Shop Pro to make mini movies. I don't want to have to start all over and learn Paint Shop Pro.