A "scratch disk" is what Adobe calls a disk where it puts any temporary files it needs. The thing is, this disk can be the same as your normal hard disk, so it's likely that the error you're getting simply means that your hard disk is getting full, and that you should free up some space. Windows itself might also remind you of that fact when it pops up a balloon saying you're running out of space.

One way you can clear space is to run the Disk Cleanup Wizard. If you go to the Start Menu, then All Programs, then Accessories -> System Tools -> Disk Cleanup Wizard, your computer will churn for a bit and then give you a window where you can select things that you want to clear up. For the most part you can simply leave the settings at their defaults and click OK, at which point your computer will do a quick cleanup of files which aren't necessary. Hopefully, you might then have enough space to load your pictures.

There's a page on Adobe's website which explains more, but it could be a bit too technical. It's below if you want to see it, though.

Hope this helps!

- Ciaran.