Most mods on the server right now are not even in 1.2.4 only 1.2.3.
This is a tough time for the minecraft modding community from what I am seeing, most major players are waiting on to see what really happens with the Minecraft server before they work on any new code. And from what I've seen as well, there are alot of code changes to 1.2.4 as is to support bukkit more, which means anything non-bukkit is broken 10 ways to Sunday.
Modloader, ModloaderMP, and MCForge when I checked 3 days ago were still only working on v1.2.3 with no plans to do a 1.2.4 release. And most also don't have plans to continue support until ~1.3 - 1.4 when ever the first stage of the Mod API hits. So most non-bukkit mods are dead in the water until Minecraft gets its API.
As soon as there is an official its working release for each of the mods I'll generate the updated XML to bring all the mods client side up to date.