Client Setup Intructions:
Download the Technic Launcher here.
Run the Technic Launcher.
Select Tekkit from the dropdown, log in.
Let it download.
You are now ready to play Tekkit
Fix for Blank Window in Linux after Login
If you are in Linux and all it gives you is a blank window after logging in, try updating the LWJGL libraries with the following script: update_tekkit_lwjgl.sh
Just download and run the script.