Hopefully simple Question...

A really cool mod has recently been discontinued by the creator, and is currently sitting at 1.1 compatibility. He has given permission for anyone who wants to use his stuff to do so. How would I go about porting it over to 1.2.3?

Depends on what the mod does and whether it modifies base classes.

1.2 introduced a new save format, jungle biome, and taller chunks. However, none of those should affect most simple mods. More complex mods might, though, but you can usually tell just by looking whether it will have issues or not.

If base classes were modified, you need to get a copy of the original 1.1 class decompiled, compare it to 1.1 modded class, and make notes on what parts were modified. Then try to make the same changes to the 1.2 version of the class. This may not work if the original class was too heavily changed with the latest update, but if that is the case then there really isn't a good way to update the mod except for studying the changes and adapting the code.

Well, what in the world is the mod?

A mod that implements Tiberium. But, thing is, it only uses Modloader classes, doesn't modify a single base that I can see. It just doesn't seem to play nice with 1.2.3.

This mod:

http://www.minecraftforum.net/topic/818488-ionsto-cnc-tiberium-mod-11/

Warning, the coder's dyslexic, so his spelling... not great, sometimes. Code's sound on 1.1 though.

Edit: Nevermind, sr and zp classes are modded.