1. Start the procedure by downloading and installing Rainmeter software.
Once you are done with Rainmeter installation, download Omnimo 3.1 skin for Rainmeter.
Extract the contents of the zip pack and then double-click on Omnimo.rmskin file to start installing the skin.
Once installed, add new panels and arrange them one by one to get the Windows 8 Start screen look.
NOTE: The developer of Omnimo Rainmeter skin, fediafedia, is working on a new version of the skin which will bring the exact Windows 8 Tablet UI Start menu to Windows 7 (with Start at the top left and user picture at the top right of the screen) and the skin will be released within a week or two.
Until then, you can follow the above procedure to get similar Start screen in Windows 7.