Does Microsoft Security Essentials replace Windows Defender?
Yes. Windows Defender protects against adware and spyware, while MSE does all that and more (protection from viruses, rootkits, etc).
MSE will actually disable Windows Defender to manage your PC's realtime protection. Also, from the Security Essentials Wikipedia page:
protected by studiohack♦ Apr 14 '11 at 20:02
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