How can I install mods for Minecraft's vanilla server?

I've seen this question answered for bukkit but not vanilla minecraft server. I've been told that vanilla minecraft does not support mods but when I go to buildcraft's main site, (http://www.mod-buildcraft.com/installation/manual-server/), it is alluding to installing using the vanilla Minecraft server. Also, he states that the bukkit version of his mod is maintained by someone else (so his server mod should be for vanilla Minecraft, right?)

I've even seen a youtube video on how to install ModLoaderMP for vanilla Minecraft server, but when I follow those directions and run the server, I get an error saying the jar was corrupt.

How do I install mods for vanilla Minecraft?

make sure you don't delete the "META-INF" for the server. this will corrupt it. also make sure you download the server mod. not the client mod