There is some mythology around sideloading apps, possibly because many IT pros have yet to experience it firsthand. In reality, the process is super simple: it is nothing more difficult than running a few commands in Windows PowerShell. There are a few requirements that you have to set up in advance though, and those too are rather easy.
You can add line-of-business (LOB) Windows® Store apps to a Windows® image by using Windows PowerShell® or the Deployment Image Servicing and Management (DISM) platform. Windows Store apps are a new type of application that runs on Windows 8 devices. These apps are based on the Windows Runtime API and differ from traditional desktop apps in their design and in the way users can interact with them on Windows 8 devices. To learn more about Windows Store apps, see What is a Windows Store App?.
Typically, Windows Store apps are available only through the Windows® Store. You can submit LOB Windows Store apps to the Windows Store and make them available outside of your enterprise. However, you can also develop Windows Store apps for use only within your enterprise and add them to Windows devices you manage through a process we call sideloading. Sideloaded apps do not have to be certified by or installed through the Windows Store.
Apps that aren’t signed by Windows Store can only be installed on sideloading-enabled devices.
Windows 8 Sideloading Requirements
You can sideload LOB Windows Store apps apps on devices running Windows RT and on devices running Windows Server 2012, Windows 8 Enterprise, or Windows® 8 Pro. You can’t sideload LOB Windows Store apps on any other editions of Windows in your enterprise. However, you can use a developer license to add apps that are in development to other editions of Windows. For more information about testing apps that are in development, see Get a Developer License.
Before you can add sideloaded LOB apps to a Windows image:
- You must enable the Allow all trusted applications to install Group Policy setting.
Before you can run sideloaded LOB apps:
- You must activate the sideloading product key on a device running Windows 8 Enterprise or Windows® 8 Pro. You must activate the sideloading product key on a device running Windows RT.
- You must join the device running Windows 8 Enterprise or Windows Server 2012 to an Active Directory domain that has the Allow all trusted applications to install Group Policy setting enabled.
- You can enable sideloading on Windows 8 Enterprise or Windows Server 2012 just by joining the device to a domain. To enable sideloading on a Windows 8 Enterprise device that is not domain-joined, you must use a sideloading product activation key.
Note: To enable sideloading on Windows® 8 Pro device, you must use a sideloading product activation key.
Until the device meets all of the sideloading requirements, app tiles on the Start menu will show an “X” in the bottom-right corner to indicate that a problem is preventing the app from running.
To set Group Policy for sideloading
1. Open the Group Policy editor (gpedit.msc). For example, on a computer that is running Windows 8, from the Start screen, type Edit Group Policy, click Settings, and then select the Edit Group Policy setting from the search results.
2. Under Local Computer Policy in the left pane, click to expand Computer Configuration, Administrative Templates, Windows Components, and then App Package Deployment.
3. Double-click the Allow all trusted apps to install setting.
4. In the Allow all trusted apps to install window, click Enabled and then click OK.
Setting the Group Policy to allow trusted applications updates the following registry setting: HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\Appx\AllowAllTrustedApps
The entire TechNet Article can be read at – http://technet.microsoft.com/en-us/library/hh852635.aspx#SideloadingRequirements