Help with custom fields!

Ok so i made a site where the users can post in 1 single category.But if they want to have a thumbnail, rating and a video in their post they have to use the custom fields.The problem i have with the normal fields is that every user can make a new custom field and thus making a huge mess.Is there a plugin or a way to add 3 fields with names (and hopefully text under them so i can explain how to use them) for video, rating and thumbnail?Here is a pic 😀 i want to remove the things in red (изтриване = Delete)

http://img522.imageshack.us/img522/2196/customfields.png

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