No, you can't change that with the File Types tab. That's what pissed me off. Under all the image file types, OPEN is the default action, and you can set it to whatever program you like. When you right-click on an image file, however, PREVIEW is the default. PREVIEW isn't even listed in options for the image file types. Only way I know to disable it is by modifying the registry.
Now if anyone knows how to make the DETAILS panel stay open in folders in Webview, I'd be eternally indebted...
Gibletpie