How Can you Get Minecraft mods to work?

(this is not an answer i am just adding to detail)

I am trying to install the x-ray mod which says it does not need modloader or anything else like that. so i do everything it says in the tutorial (open minecraft.jar, delete meta-inf, drag in the files) but when i start up minecraft nothing happens, it plays minecraft as if i had not installed the mod in the first place. Am i doing somthing wrong?