How do you change a TES File to a TES Plugin (.esp)

I have vista

What's a TES File? If you mean a .ESM (Master file), then why would you want to change it into a .ESP (Modded file that relies on the ESM(s) uses in construction of the mod)? I'm sure you have your reasons though, so the more relevant tools you may like (lifted from http://cs.elderscrolls.com/constwiki/index.php/Esp_vs._Esm page of the wiki) are:

• http://cs.elderscrolls.com/constwiki/index.php/TES4Gecko - Esm/esp conversion; Merge esp into esm; Mod Splitting; Remove Masters; etc.
  
• http://cs.elderscrolls.com/constwiki/index.php/TES4Edit - Remove masters; Copy records between mods; etc.
  
• http://cs.elderscrolls.com/constwiki/index.php/Wrye_Bash - Esm/esp conversion; Esmify/Espify masters; Bashed Patch; Disable Masters.

Also, you mentioned vista? If you mean the game won't work properly, or there's some sort of error with your .ESP/.ESM's, then try reading http://cs.elderscrolls.com/constwiki/index.php/Windows_Vista.

Did any of that help?