I am a CAD modeler and I have a real need to view .stl files in the viewer. I am not adept at writing code but can fumble through and learn some basic things if I need to. I have not found a plug-in that will work for this yet. Is there a plugin that will work w/ DOpus to view .stl (stereolithography) file formats? If Not, Is there a way to link DOpus to an external stl viewer? If Not, is there a simple to understand way I can wright my own code for a plug-in 
Thanks
If there is a preview handler that can run in Windows Explorer or Outlook, then that should work in Opus as well.
If there is an ActiveX control that allows Internet Explorer to view the files, that can also be made to work with Opus easily enough (in most cases).
Otherwise, you're probably looking at having to write a custom viewer. I don't know the file format so I don't know how difficult that would be. Writing the viewer itself would be a lot more work than the Opus-specific parts, which are simple by comparison.
I have installed a viewer for DWG files compatible with activex with success, so I know my way around enough to do that, however I found an online source that gave me a set of directions to follow.
So now I have 2 questions, 1) how do I know if a viewer will run in widows explorer? and 2) If it is compatible, how do I install it so it works with active x? or at-lest where do I find the info to guide me through the processes?
The web pages for viewers typically tell you where they can run, but it depends on the viewer. If they don't mention Explorer, Outlook or Preview Handlers then they probably don't provide a suitable preview handler, but the only way to know for sure is to install them and see if you can view a file in Explorer's viewer. (Or to ask the authors of the viewer directly.)
ActiveX is potentially more complicated, and varies by viewer. You would have to ask the viewer authors; we can only help with the Opus specific side of things (e.g. if something provides either type of viewer but it's not appearing in the Opus viewer pane, then we can help; but we can't in general guess how to install someone else's ActiveX control, at least without knowing which specific control we are talking about.)
Thanks for your response this is extremely helpful for my learning curve here!
1 more helpful insight before I leave you alone,
---- theatrically if I were to install a viewer called openSTL onto my desk top, and add .stl to the internet exploror 32bit through activeX it would probably run through DOpus give or take a few defult settings here or there? Or am I missing anything important?
If you can get it viewing .stl files in IE then it should be really easy to get that working inside Opus as well (since we can use IE as a viewer, or a viewer proxy if you like). We can help with that part if you get there.
Great! Thanks so much for your help! 
You just need to install MicroSoft 3D Viewer. It then is used automatically by DirOp if file is STL. Its a miracle, I know, but MS have actually already solved the problem!