This is how to fix the Update Failed error if you are trying to install Tekkit via the launcher (windows):
1: Go to: *snip*
2: Click on the drop-down and set it to minecraft 1.1
3: Click next, it will begin a download
4: Once the download is complete go to %appdata% then go to roaming, then .techniclauncher
5: Go to tekkit and then bin
6: Move the minecraft.jar to the bin folder (make sure it is called minecraft.jar)
7: Run the launcher, it should work
8: Reply to this topic if it worked or what the error you got was
9: Thank me