Server question.

Some do have multy versions altought you need to instal modloader :|

a server and a single player mod are different things. a survival single player mod needs only change what happens on the client side(mine craft you are playing on your computer).

however with a server mod you need to note a few things.

1. mods will not work on the vanilla server. you will need a alternate server software like bukkit.

2. with a server mod you need to be sending data from both the client (your screen) and the server(the server you play on in multiplayer). a server mod can be a few things, from adding new functionality to an existing item or adding new dynamics to the game. what won't change however is the client side. a server mod can only effect what the server sends to your client. it cannot change the functionality of the client.

so basicly ssp mods are client side and don't need to be sent over network where as server mods can alter or add to what the client can display but cannot change the client functionality

soon when the mod api is released we will be able to add to the client through server mods

hope this has helped