The registry contains everything that makes your computer work. If you change something by accident you can really screw things up to include your computer not even working at all, which is why caution is advised. Basically follow the instructions to the letter and you won't have any issues.
Like I said, the fix is for Windows 7 and SHOULD work for Win 8. You might want to check out The Win 8 forums for more up to date info and fixes.