I am trying to upgrade 10.6.8 to 10.8.2, yet I am having problems doing it. I think part of the reason might be because I have very little free space on my hard drive. I have not found any specifications for what the minimum amount of free space is, but I thought it was going to be 8GB, and it turns out that having 8GB free didn't solve the problem. I have gotten down to 0 before on my computer for free space in Finder, but for some reason, the partition's available doesn't seem to agree. I also get the error message "This disk can not be used to start up your computer" when I try to upgrade from the app store download installer. Is this because I have rEFit installed and dual boot Linux? Is it because I don't have enough free hard drive space? Everything is backed up, and I hope that the 10.6.8 backups aren't removed from the Time Capsule I use once I do get this working. Does anyone have any advice or suggestions?