scratch disks

ok im a total noob at photoshop ive benn using paint shop and animation shop. I got down how to upload brushes and getting them on photoshop. But whenever i try to use them or even one of the normal brushes they provide i get Scratch Disks are full or something like that. What do i do?

I've never even heard of that problem...?

Maybe post a screen shot of the error message.

I think Photoshop uses a scratch disk only when there is not enough RAM.