How to make Lion images under OS X Server (10.8.4) for NetInstall?

Hi there,

I am running OS X Server (10.8.4) on a Mac Mini (Early 2009). I have succesfully created NetInstall-images for Mountain Lion (10.8.4), but I am running into problems when I want to create a NetInstall-image for the computers that can only run Mac OS X Lion (10.7). I have downloaded the installer for Lion from the App Store, but it is not recognized by System Image Utility (SIU). Also when I extract the InstalESD.dmg from the installer-package and mount it, it is not recognized by SIU. What am I doing wrong? And if not, what should I do otherwise to get working NetInstall-images for Lion?

Many thanks in advance,

Jannem