VNC isn’t packaged as an MSI, and so it’s a little tricky to deply via Group Policy - however it’s not impossible. Here’s how to do it…

1. Grab http://www.bozteck.com/Downloads/realsilent.zip and extract to \\servername\clientapps\RealVNC 
2. Ensure that Domain Computers (or a group containing all domain computers, such as Authenticated Users) has access to the share / folder 
3. Replace the contents of the .reg file with the following (need to replace the password with your preferred password in hex - the easiest way to get this is to install it yourself, set the password and then grab it from the registry)

   Windows Registry Editor Version 5.00
   [HKEY_LOCAL_MACHINE\SOFTWARE\RealVNC\WinVNC4]
   "Password"=hex:<password in hex>
   "SecurityTypes"="VncAuth"
   "ReverseSecurityTypes"="None"
   "QueryConnect"=dword:00000000
   "QueryOnlyIfLoggedOn"=dword:00000000
   "PortNumber"=dword:0000170c
   "IdleTimeout"=dword:00000e10
   "HTTPPortNumber"=dword:000016a8
   "LocalHost"=dword:00000000
   "Hosts"="+," 

4. Create a file in the directory called install.bat, and insert the following (adjust to suit your environment)

   @echo off
   cls
   :checkifinstalled
   if exist "%programfiles%\RealVNC\VNC4\vnc_installed.txt" (goto end) else (goto installvnc)
   :installvnc
   \\sbs-svr\clientapps\RealVNC\RealSilent.exe
   date /t > "%programfiles%\RealVNC\VNC4\vnc_installed.txt"
   :end 

5. Now, create a GPO, and add the aforementioned install.bat as a Computer Startup Script (as opposed to a login script. A startup script won’t require users to have local admin permissions). 
6. Add the GPO to your OU(s) containing all PC’s 
7. And finally, modify your Group Policy to allow RealVNC through the firewall when using the Domain Profile. This setting can be found here on an SBS Server:
   ComputerConfig => Administrative Templates => Network => Network Connections => Windows Firewall => Domain Profile => Windows Firewall: Define Port Exceptions
   Enable this policy, and add the following:
   5900:TCP:*:Enabled:RealVNC - Port