Hello, I'm a bit of a computer dummy, so I don't know where to find information on this. I have a macbook I bought about 5 years ago, and it's upgraded as far as it will go at 10.5.8... anyways, I really want to be able to play tekkit with the boy I babysit, but when I try to open the .jar it just says it can't be launched... what do i need to do??? please help