.WTF files always open with notepad

I was going to join a private WoW server, and to do so one must change the "realmlist.wtf" file, I opened it with notepad and changed it to the appropriate content (wich was set realmlist xxxxxxx (xxxxxx stands for the servername)) now every time I try to open World of Warcraft it will not connect due to not being able to use the realmlist.wtf file since now all .WTF files open with notepad (.wtf files used to be opened with an "unknown application). So in short here is my question:

What are realmlist.wtf files supposed to open with?
How can I change that?

They are not supposed to open with anything. Are you sure that while you were editing the files,you didn't make them .txt?

Do the right thing and disable hiding file extensions (if you haven't done that already).

There are numerous references to editing the WoW .wtf files using Notepad;

eg: http://www.wowinsider.com/2007/03/28/wtf/

I suspect that when you did you left the 'Always use the selcted program to open this kind of file' box checked.

Look under Windows Explorer, Tools, Folder Options, File Types for wtf and if it is there and uses Notepad to open it then delete that entry.

Thanks a million guys