Despite Apple's claim that Mac OS X 10.7 Lion can only be installed as an update from Snow Leopard, you can certainly install Lion on a clean hard drive. Once you download the Lion installation file through the App Store, you can create a boot disc on either a DVD or a USB drive.
Here are a few screen shots of the process.
The highly anticipated next major update of Mac OS X, Lion is given the Golden Master status today. The official build is 11A511 as shown. Developers can get their hands on this release as early as this morning on the first day of July. Apple is right on schedule with its promise of making OS X Lion available through the App Store sometimes in July. My guess is everyone will see this update in a week or two.
I'm off to check out all the new features Lion has to offers!