DWGicon.dll is a Windows shell extension that enables you to identify the version of a drawing just by looking at its icon in explorer. You don't need to have CAD software installed on your machine for it to work.
R15 drawings will displays the current icon for R2000 drawings. All other drawing file versions have the revision number in it. Invalid drawings have a question mark. New drawings (R2001 and later) will show a yellow star. If you see that, it is time to get a new version of DWGicon.dll.
DWGicon also works great in FileOpen dialogs. A good example is your CAD software's very own FileOpen dialog: chances are it gives no information on a selected drawing whatsoever (apart from the preview and the name of course).
DWGicon.dll has been tested on Win95/98/Me as well as NT4/2000. This version replaces version 1.0 which produced errors on some machines. The current version is more robust and has debug facilities built in.