This recent OBuild Factory post indicates there will be no further efforts to build Open JDK 7 on OS X 10.6: https://github.com/hgomez/obuildfactory/issues/3 It looks like rolling your own Open JDK 7 got a lot harder.
Team Cupertino changed the game this time around by providing its next major release as a download-only upgrade. This guide will focus on getting a typical Mac that meets recommended system requirements ready for a standard download and upgrade of Lion. First we need to determine if the Mac(s) being considered for upgrade are going to meet Lion's minimum system requirements.
Apple suggests that you have: To determine if you have the suggested system requirements, open up the About This Mac pane by clicking on the Apple Icon in the Menu Bar. Here you will see your processor type, system allocated memory, and the installed version of Mac OS X.
System Information can be found in the Utilities folder within the Applications folder, or you can click the Apple icon in the Menu Bar, select About This Mac, and click More Info.
Once open, scroll down the left hand column and select Applications.
Is it possible to update my i Mac running OS X Snow Leopard to Java 7?