After install of Security Essentials I see that Defender is diabled, not triggered, should the same not be done for UAC?

No. It's two completely separate things.The reason that Defender is "disabled" is becase MSSE uses the already-existing Defender scan engine. Having two apps using the same background service... well, that wouldn't be good.Long story short: Defender is still there, and is still actuve. Its interface is merely disabled, because it's now managed by MSSE.HTH,Chris[If this post helps to resolve your issue, please click the "Mark as Answer" or "Helpful" button at the top of this message. By marking a post as Answered, or Helpful you help others find the answer faster.]

In one word, function of Windows Defender is included in Security Essentials. In order to avoid confliction, it is disabled as MSSE is installed. It is the same when using OneCare in the past.

Great that Defender is disabled, question was Why not disable UAC? If there is anything useful that UAC does, put it in Essentials or is it not partly there already? But let me disable the partthat every time Windows Media Player starts, one is forced topopup response.

UAC will help check if a program is trying to use administrator permission to do any action. It is not the same function as MSSE since MSSE is an antivirus program. Of course if you prefer disable UAC, change the UAC level to Never notify.