Quote from Pyroglyph
I've placed the IC2 jar in the mods folder (the mods folder being alongside the src, eclipse and bin folders etc) and it's not even loading when I test Minecraft. Have I put it in the wrong place? I have no idea.
Yes, that's the wrong place. The 'mods' folder is a folder inside whatever directory you assigned as the working directory in the run configuration; for most people, that is "YourMod/eclipse/", in which you will generally find the following folders: assets, config, logs, resources, and saves. Put your 'mods' folder in that 'eclipse' directory along with the rest, and it will load any mods in there when you run your mod through Eclipse.