How can I enable concurrent Remote Desktop Sessions in Windows 8 Pro?
We'd like to do this just like we have on Windows Server 2003.
There is no official / approved way to do this.
Multi-user Remote Desktop (aka Terminal Services) is only supported on Server versions of Windows, and then only with the appropriate client access licensing.
There are 'hacks' for Windows 7 which modify the Terminal Services DLL to allow multi-user access.
None of these 'hacks' are official or licensed, and I've not (yet) seen one for Windows 8.
Actually, it's amazing how many people believe incorrectly. You CAN do concurrent sessions, initiated from either end, using RDP, it's called "Remote Assistance". What seems to confuse people is the difference in UI. "Remote Desktop" aka "MS Terminal Services Client" (mstsc.exe) is used for TS connections to give someone the ability to remotely access their terminal. Multiple people using the same terminal implies something else and though a few people might need it outside of a support scenario, most do not. MOST people are looking to offer remote assistance (different concept, different ui, exact same technology). RA connection support is also available on all versions of Windows while MSTSC is not available for more basic editions such as home (even if the client is, the RDP service will not respond to TS connection attempts by default).
The easiest way for admins to launch RA is with the below command (save it as a shortcut). The only catch for most of us looking to do remote support, is that you'll want to setup a group policy to allow for these unsolicited connections (remote assistance offers) otherwise the user must request assistance via any number of techniques. Additional useful links available below.
P.S. Before you vote down and/or argue about how this isn't what's being asked for, go do the research. "Shadow sessions (multiple TS connections to the same terminal)" were once possible using mstsc and effectively accomplished the same thing, but they are a different concept and support has been discontinued. RA connections will accomplish what's generally sought, are the proper way to do it, and are fully supported for the foreseeable future. If on the other hand, Terminal Services is what the OP really meant (multiple individuals running their own terminal sessions simultaneously), then it is true that the desktop editions of Windows do not support this, never have and never will as Terminal Services requires a special licenses model (though you CAN get away with a limited number of TS connections to Windows Server Editions). There are patches that will cause even the desktop edition of windows to respond to both TS and RA attempts but as others have said, they are hacks and not official.
There is now a patch for Windows 8 but as the other users said, there is no official/approved way to do this.