Mac OSX - Install Failed
The Genius Bar will reinstall your OS and/or diagnose any potential hardware problems at no charge regardless of warranty status.  The only time they will require a fee is if your Mac is indeed out of warranty and requires a hardware repair, at which time you would need to pay in order to have the repair performed.

If visiting an Apple store is an option for you then by all means don't let your warranty status stop you from visiting.  They should be able to install 10.6 since it came with your Mac and/or 10.8 if you can show proof of purchase for it.

For the actual question, you can view the log file while performing the installation under either File > View Log or View > Log, I don't have an install in progress at the moment to reference.  One of those should show you the log from the installation which would hopefully give you a reference as to what part of the installation failed.