Added.
Server is now back up, on 1.2.
You need to have the 1.2 client to log in. If you haven't already updated to 1.3 this should just be a case of using the new launcher and NOT UPDATING TO 1.3 when it asks you.
If you have already upgraded, you need to find the old 1.2 version of Minecraft, and launch it with the new launcher and NOT UPDATE!
I think I have 1.2 on my PC actually, lemme check.