Offline mode not working?

[alekthefirst]

How do i get to play offline?

i read somewhere that i have to log in with a minecraft premium acc to unlock offline mode on a pack. so i have logged in with a premium minecraft acc on Tekkit (the 1.5.2 version) Big Dig, Hexxit and Voltz. but neither of these packs are working without a internet connection. (but they all work with internet connection)

I press the "launch" the button goes dark grey, and after that nothing happens, other than me pressing it a few more times, of course. every time i press it the launcher seems to "hang" (stop) for a few seconds before returning to the normal "beeing able to press buttons" state

I may also mention that no pictures (other than the standard technic backound) are seen, but that can be related to not having a internet connection