I'm not sure about previous versions of Windows, but Windows ME has a feature which can make all the pictures in your "My Pictures" folder become your screensaver (the screensaver cycles through the pics). To change your screensaver to the pictures in your "My Pictures" folder, right-click on your desktop and click properties. Then, go to the screensaver section. Scroll down the screensaver list until you see the screensaver titled "My Pictures Screen Saver". Click on it, then click apply, and you have it. Of course, for the screensaver to be about knives, your "My Pictures" folder must be full of knife pics.
Also, you may be able to download a free screensaver program which is programmable to your picture choices. To find such a program, I'd do a search on a good search engine.