Windows Vista introduced the Preview Pane in Windows Explorer, which shows the contents of the currently chosen file. You get to see a preview of the files contents on the right hand side of your Explorer. You can also play multimedia files from the Preview pane, without opening Windows Media Player.
The preview pane is enabled as follows : Organize > Layout > Preview Pane.
Add More File Types To Explorer Preview Pane
If you wish, you can add more File Types to Windows 7 and Windows Vista Explorer Preview Pane with PreviewConfig Utility. If you have a custom file type; and wish to register a plain text or a multimedia preview handler, for this custom file type, you can do so using this utility.
To use this tool download and run PreviewHandler utility with administrative privileges. Next, select the file type from the listing, and choose the type of Preview you want for this file type – eg Media, Plain-text, None. Finally click Apply.
Do read its ReadMe file first before using it.