As it turns out, it was WAY easier then I thought.
I pasted it here to avoid link rot...
How to Get Started with XenCenter
New Ranges of Portable IP Addresses (Public and Private) that are Routed as "Secondary on VLAN". This example solution to the setup of a new VM requires that you have usable IPs available on the Private Network.
Note that your server will come pre-configured with a variety of templates that will allow you to be off and running with XenServer in very little time.
The very first thing that you need to do is make sure that you are connected to the SoftLayer Private Network via VPN. Establish a connection via SSL VPN or PPTP and we will get started.
Open up XenCenter and click on "Add your XenServer".
You will be asked for your server's Hostname, your User name and your Password. You need to use your server's Private IP address (Looks like 10.x.x.x), the User name "root" and then your server's root password. This information is available in the portal by going to the following URL and then clicking on the name of your XenServer. Once you have all of the relevant information entered, click on "Connect".
You will be presented with a screen that allows you to get started working with Virtual Machines. If you receive a Free License activation screen, please take time to complete this now.
We are going to jump right in, so let's get started and create our first Virtual Machine. We will Create a CentOS virtual machine with a disk of 10 GB and we will have both our Public and Private Networks functioning. Right-click on your server's name and then select "New VM...".
The wizard asks us to "Select an operating system for the new virtual machine". The templates are self-explanatory but remember that some of them will require that you provide your own media. Because we are using CentOS, you can use SoftLayer's private mirrors for CentOS to get our installation going. We select a version of CnetOS and then click on "Next".
The wizard asks us to, "Enter a name and description for the new virtual machine". This is truly just a name so call it what you like and feel free to describe it for later.
The wizard now asks us to, "Enter the location of the guest operating system installation media". In our example, we can use SoftLayer's CentOS mirror as installation media. We need to provide an Install URL of:
*A trailing ‘/’ at the end of the URL like in the image below will sometimes break the install.
Fill this in and click on Next.
*This mirror is only available on the SoftLayer Private Network.
We are getting closer, the wizard is now asking us to provide some simple hardware allocations for the system. We can "Set the number of CPUs and the initial memory allocation for the new VM". We are going to build a quite streamlined system and we don't need too much RAM so 512 will be more than enough. Click on Next to continue once you have chosen your limits.
On the next screen we can "Enter information about the virtual disks for the new virtual machine". It is time to allocate disk space to your VM. Please remember that this is like adding hard disks, it is not like partitioning your system. Partitioning is done during the installation of the OS. The default size is 8 GB for this particular template which is more than enough for the name server that I am building. Feel free to make the disk larger according to your needs by highlighting the disk and clicking on "Edit...". Once you are done, click on Next.
You can now "Add or remove virtual network interfaces for the virtual machine". The defaults should be acceptable unless you do not want your system to be able to communicate on the Private Network. Our example requires that you leave both interfaces in the system, but an experienced Xen Administrator can remove one of them for their own purposes. In that case, you may highlight and delete an interface if you like. Click on Next when you have it the way that you need.
If everything went okay, you will now be at the screen that says that "Your new virtual machine configuration is complete". We will leave the check in "Start VM automatically" and click on Finish to immediately begin the installation of CentOS. Once you click this, you will be dropped back to the main screen, but you will notice that on the left-hand side of the screen you can see your new VM listed.
Select your new VM and click on the "Console" tab. You can now see that your system is booted into the CentOS installer awaiting your input.
All of the parameters of a CentOS installation are outside of the scope of this article and will need to be customized by your System Administrator, but this article will provide some specific pieces of information that you need to complete the installation. Select your language to get started. The CentOS installer will then ask you for assistance in configuring the Networking Devices in the system. Select "eth0 - xen Virtual Ethernet" and click on OK.
In the pre-requisite notes, we made sure that we already had a set of Portable IP Addresses routed as "Secondary on VLAN" ready for this installation. Make sure that you have the information ready for the "Configure TCP/IP" step. We need to manually configure the interface with IPV4 support and disable IPV6 support for now.
Using the information available from the KnowledgeLayer (Static and Portable IP Blocks) I am aware of how to use my Private IP Subnet which is 10.17.37.240/29. Click on "OK" and you will immediately be taken to the CentOS installer if you entered all other options correctly. At this point you and your System Administrator can perform the installation of CentOS as per your own guidelines.
The next stage may hang as it is loading data from the mirror but should indicate that is it retrieving something. If it errors out, check that your subnet is a portable subnet and that you have properly entered it in not using an IP that is already in use. If you are still having issues, please feel free to create a Support ticket. Our Support team is not responsible for creating VMs for our clients, but we will gladly look into your issue and assist in any way we can to get you started.