I bought a new rMBP last month and received a redeem code for Mountain Lion. Now I am trying to upgrade my Late-2009 MBA, which is still running a Leopard system. However, I copied the InstallESD.dmg from the installation package to this Leopard machine and it cannot be mounted, not to say restoring it to a flash disk. Is it because the system is to obsolete that cannot read newly released dmg files? This mba is in my another house and I didn't bring my new rMBP here. so the InstallESD.dmg and a Leopard machine is all I have here, please please give me some advice!