You should only install Forge, thus
QuoteRisugami's ModLoader (Only needed for IC² 1.81 and earlier versions)
After you install Forge, you simply need to drag the IC2 jar into the mods directory. That's all there is to it. Just make sure you have the correct MInecraft version (the current public build of IC2 is for 1.4.5, not the latest version, 1.4.6), and the correct version of Forge to go with it.