I succesfully installed Step 7 lite on windows 7 but was an Virtualization technique, which consist in using Virtual-PC (the package for using diversing OS environment), firts one must to downloading Virtual PC and after that the OS system itself, then i did downloaded Windows XP Mode (for Windows 7 32 Bits), (all of that is free of charge, as well as Step 7 Lite ).
With the virtual enrionment setted allready, can install Step 7 Lite SP 4.0
Hope this could be helping notes, Regards!