Most applications rely on some sort of secondary windows. In most cases, those windows are either modal dialogs or non-modal property pages. Either of these are possible within MMC, but where possible it is suggested that non-modal property pages be used. Modal dialogs should be used only where it is necessary for a decision to be made before proceeding on to anything else. Property pages in MMC work like they do in the shell, with one major exception: property pages in MMC should always use the standard shell large size (252x218 dialog units), for four reasons:
Uniformity - all property pages will be a standard size.
Aesthetics - enforcing this will prevent some property pages from being short and wide and other tall and narrow.
Simplicity - it is simplest for Snap-In providers to work with extensions of dialogs of a uniform size.
Performance - we don't have to first ask each extension what size it wants and then create a property frame.
One other difference is that your property pages have the possibility of being extended by other Snap-Ins, if you allow it. This allows extension Snap-Ins to use your objects as the mechanism by which they configure themselves.