Since Mac OS X Lion is not being installed via disks, it's via download. There isn't a assigned way to clean install yet. This is the only way right now. I'll try to find a way to clean install with only one computer not two. 1. On the Mac you want to clean install, open System Preferences, and go to and click on Startup Disk. 2. Click Target Disk Mode and connect your Mac to another Mac via Firewire or Thunderbolt (Fastest) with the OS. 3. Boot off the Mac OS X Lion installer partition on the clean install Mac. 4. Wait until the install finishes, and your Mac will be clean.