If you are installing a Linux distro as a XenServer guest OS for the first time, you will notice that by default the installation will start in non-GUI mode and you will not be able to easily customize the packages to be installed. There are couple of ways that you want do this, one of which is described in CTX133114 where you can add “text” parameter to the Advance OS boot parameters for CentOS 6. I have not tried this yet, but what has worked for me for installing RHEL 6 is to use the “vnc” parameter instead.
When creating the Linux VM using XenCenter, on the “Installation Media” step, there is the Advance OS boot parameters field on the bottom:
You just need to add “vnc” to the parameters. Once the VM is booting up and the OS is initializing, you should see the screen below showing that VNC has started and ready for connection. Next, assuming that you have entered a valid IP during the OS install setup, just start a VNC client and connect to the address to see the installation GUI.