This topic has been covered publicly already. Nonetheless for completeness of one my previous posts, I want to provide you with this step by step manual to a virtualized Lion.
Open your Mac App Store. Search for the keyword
Lion and choose install to download the latest build.
After a few minutes
Lion is installed as an application and waiting to get run. Go to Applications and right-click on Install Mac OS X Lion. From the drop-down menu select Show Package Contents.