I am about to replace the Hard Drive in my Macbook Pro, as my current hard drive is making crazy noises and I was told it could crash at any moment... I have an external hard drive that I have been using time machine on to keep all of my files backed up. What I'm wondering is if it is possible to use that external drive and time machine to install OSX on my new internal hard drive? I recently moved out and I realize now that I forgot my original installation disk that came with the computer. I currently have OSX 10.6.8 (I don't think this is the newer lion or mountain lion version?) If I install the new drive and boot my computer with the external plugged in while holding the option key, will it give me the option of installing from the external? Or do I need to make a bootable drive.. I'm very confused.