MultiMC is a third party launcher which lets you create and install mods on different instances (separate copies) of Minecraft. MCF Thread
In the coremods folder, of course, if that's what they were for 1.5.
EDIT: Ninjad.
And also-
!!!!!!
Well, it might come back when:
The Mod API comes out, and a release of Industrial Craft comes out for that.
Abalaka starts a new Industrial Craft project, perhaps open source to ensure future updates.
As I understand it, the way the launcher works was changed to a better and entirely new system. To support 1.6 would be to support everything following it. (As well as everything before.)
Can't blame you. KSP is awesome. I was just thinking it would be fun to do something that we, your viewers, could join in with, and OTTD seemed perfect! (Maybe I like trains too much)