Thank you for writing.
Currently, the RadBrowseEditor is meant to open only the standard OpenFileDialog and the FolderBrowserDialog. If you want to open your custom dialog you will have to use your custom editor. As we constantly try and improve our controls, we will add this idea when we plan our future releases. We will also increase its priority if other users ask for it.
I hope this clears thing up. If you have further questions, I would be glad to help.
the Telerik team
of RadControls for WinForms is available for download
(see what's new