UAC is a great feature of Windows Vista, but often leaves the user with a poor end user experience. This is often because the screen flickers when switching out of Aero and into the Vista Basic theme (for security reasons).
To help keep the majority of UAC's security features, but greatly improve the user experience, you can disable this flickering:
1. Click Start and then Run.
2. Enter secpol.msc.
2. You should see the Local Security Policy MMC:
3. Open Security Settings --> Local Policies --> Security Options
4. Scroll to the bottom of the policy list and double-click "User Account Control: Switch to the secure desktop when prompting for elevation"
5. Disable the policy and click OK.
You now won't see a mode change (flicker) when the UAC prompt is displayed.