How to find COM interface definition for given interface GUID?

I have a COM interface GUID but I don't know that interface definition. I don't know what methods it has, what parameters they have and so on. How can I obtain such information? Is it possible in general?

Practical problem is obtaining interface definition for few COM interfaces defined in actxprxy.dll. For example IFileDialogPri开发者_开发技巧vate ({AC92FFC5-F0E9-455A-906B-4A83E74A803B}). (Obviously the interface is not documented and the name does suggest there is a reason for that.) I tried to use OLE/COM Object Viewer (OleView.exe) for that but wasn't able to get the interface definition.

I am trying to implement IFileDialogPrivate while doing some experiments on forcing IExplorerBrowser control to filter Windows 7 library folders. IFileDialog (which seems to use IExplorerBrowser) does it somehow and IExplorerBrowser askes service provider for IFileDialog and IFileDialogPrivate if ICommDlgBrowser is provided so I tryied to explore that interface. (Also it asks for few other interestingly named interface - could be useful).