In my experience .tpl files are formatted in HTML. You could try renaming the file to .html editing and then renaming back to .tpl.
Alternativley you can edit .tpl files in Notepad, Wordpad etc...
Does this help?!? I Use dreamweaver 2004 MX and it allows me to open .tpl's for editing but it appears you've alreay tried that 🙂