If you messed up a Mod Installation, all you have to do is 'Force Update'. Optifine is very simple to install. I suggest downloading the "Ultra" version, as it has all the features. You HAVE to make sure you download the right version. (Some sites may advertise an outdated mod as an up to date mod) Just delete your 'Meta-Inf', and drag all the optifine files into the Minecraft.jar. That should take care of any misunderstandings you have.