I had a similar problem with Maximizer. What you need to do is look inside your WoW/WTF direcotry and find the config.wtf file so you can edit it. There is a resolution setting in there (just look around for it - it's near the top) and set that to whatever you wish to run WoW at. Note that this doesn't work all that well if you're running more than 1 resolution outside of the same WoW directory.