From the update 1 page back, the mod requires forge/fml - it doesnt need mlmp anymore, therefor its smp ready for 1.2.5 with forge.
From the update one page back,
I had some trouble decompiling IC2, so the client was ported from the obfuscated 1.90-1 version, and the server is only for CraftBukkit (didn't make a vanilla server version, sorry about that). Let me know how it works