you can either create them from scratch exactly how you want in any programming language like VB or C++, or you can use some pre-made tools to make some for you.
Flash ScreenSaver Builder Free
Flash Screensaver Master $29.95
Flash Jester $99
Screen Saver Producer $59.95
Active Screensaver Maker $29.95
Easy Screensaver Maker $25
Screensaver XP $29.99
ScreensaverMaker $24.95
Easy Screensaver Creator $24.95 
/ 
