Currently Being ModeratedSep 6, 2013 5:46 AM (in response to Volkscab)
Two steps to begin with.
Check (through 'about this Mac' ) how much RAM memory you have. You need a minimum of 2GB but 4GB would be better according to most people here. Once the memory is sorted out ... try again. If it still doesn't work ...
Update your system using the 10.6.8 combo updater ( it could take 40 minutes or more) and when finished run software update to update your itunes and security.
Then try to download Mountain Lion again.