I have read some posts here, it's said that radeditor simply call MOSS Asset Picker dialog and insert the return value to the editor content. -
This is exactly how RadEditor for MOSS uses the OOB asset picker dialog. Unfortunately I can not provide you with information on how to edit this dialog. I suggest you to address this question in some SharePoint related forum also, as this is an OOB SharePoint functionality.
the Telerik team