I'm wanting to make a bootable copy of my Mac's hard drive in preparation for the upgrade to Mountain Lion. My Mac's hard drive is 320GB; I have an external hard drive that is 250GB. Is there a way to do this on the Mac? I'm willing to pay for software like Carbon Copy Cloner if that's required.
Carbon Copy Cloner would do exactly this for you. The catch is that you can't be using more than 250GB of the 320GB HD. If that's that case, you should be fine (clone it over and upgrade).