1) clean the dust out of your fans, like the other people have been suggesting. Buy a can of compressed air for 3 bucks at home depot, and go to town on every opening your computer has.

2) Buy a laptop cooling pad. Something along these lines. There are cheaper ones than the one I linked (which is just for example's sake), and, from what I hear, they help.

3) You can try limiting the framerate of your game, which will cause the graphics card not to work as hard. You can do this with the command: /console maxfps 30 typed directly into your chat window. This will, of course, set your maximum framerate to 30 frames per second. Note that this will only help if your computer exceeds WoW's recommended specs (which is likely, since WoW is an old game). If you want to see what your framerate is at any given point, type CTRL-R to turn on the framerate display. If the number you see is consistently above 30, then limiting the framerate to 30 should help. It may make your game somewhat less smooth (you can try setting the maxfps higher if you want), but there's a good chance it'll help with your overheating issues.

Anyway, if none of the above help, then it's likely something is wrong with your laptop. Maybe you have a fan that broke, or a heatsink that has come a bit loose, or something. There's just no way that a clean computer on a cooling pad playing WoW at half-throttle should overheat.