Do you mean you want certain folders -- or any/all folders that contain mostly certain filetypes -- to be shown using thumbnails mode while other folders are shown using list mode?
You can do that using Folder Formats and either Path Formats (if you want to explicitly set the formats of certain folders) or Content-Type Formats (if you want the format to change automatically based on the types of files in each folder). See the Folder Format guides for more information:
[ul][li]Folder Formats: Quick Guide[/li]
[li]Folder Formats: Special Folders (Computer, Network, etc.)[/li]
[li]Folder Formats: Detailed Guide[/li][/ul]