I already have Snow Leopard installed on my imac. I am trying to reinstall snow leopard on my imac so I can wipe it clean and sell it. It tells me that it cannot be installed on my computer. I do not use PGP. Also, I followed your pointer and when i hit apply to partition the disk I get "Partition failed with the error: Could not modify partition map because file system verification failed". Anybody know what other steps I can take to get this resolved?