Windows 8 comes with lots of new changes, it comes with a new Aero Lite theme which comes with square borders for explorer, Microsoft has removed basics themes from Windows 8 too.
If you had loved the new cleaned and minimal Aero Lite theme which is featured in Windows 8 Consumer Preview then you can download Aero Lite Beta for Windows 7 created by sagorpirbd @ DA.
This theme comes with Visual Styles/Themes, Explorer.exe for (32Bit & 64Bit), Start ORB Image, shell32.dll (32Bit & 64Bit), and Wallpaper.
You can use following link to download it :-
Download Aero Lite Beta for Windows 7