The new Windows 8 consumer preview is loaded with a new improved security system known as Windows Defender to provide you better protection. This tool is better then the Microsoft Security Essentials so you don`t need to consider installing or keep MS Security Essentials on your windows8 system. Security essentials did`nt work when installed on most of win8 systems, however it is still good for people using another version of windows like Windows 7, Windows xp and Vista. It is recommended to not have Security Essentials on windows 8 because the security system Windows Defender of windows 8 is greater then security essentials.
See what Microsoft says about Security Essentials:
Microsoft Security Essentials will not be needed on Windows 8. We remain committed to providing strong protection of Windows 7 and earlier Windows users with Microsoft Security Essentials. Both are based on the same core technology (engine, signatures, filter driver), but Windows Defender on Windows 8 also provides additional functionality, such as integration with Windows 8 secured boot.
Moreover, you can go to the HELP menu of Windows defender and check the ABOUT page. It says everything you want to know. It dose not protect you only from spywares but it deals with viruses and malwares as well. Compare it with MSE and see whats difference and new in windows 8 defender.
So you can make a comparison between Microsoft Security essentials and the windows 8 defender features. After seeing this, you wont need installing MSE anymore on windows 8.