Setting up a Citrix Xen Server is very easy, however do you have to consider design before start to deploy a Citrix Xen Server farm.
First , I would like you to think about networking. For a single server, one nic is enough however if you want to grow your farm and add servers to your pool you should have to use a second nic. Why??? well if you are going to use share storage in a pool of server (pools only make sense with share storage) Citrix Xen will require to have a nic for management and a second nic for storage. The storage nic can be shared for VM network traffic however it is not recomended for production enviroment.
Citrix Xen Server standalone = 1 NIC
Citrix Xen Server Pool (shared storage) = at least 2 NIC , For production enviroments at least 3 NIC
Second , make sure that you have a 64 bit processor. In addition, remember to enable VT on BIOS so you can create paravirtualized Guest OS. Paravirtualization can give you a lot better performance.
Third, make sure you have a lot of memory. Basically, memory will limit the quantity of VMs that you can create. You can over provision memory however the overall performance of the virtual machine will be affected because VM memory will require to swap on disk.
Now, we have our server ready to install so you have to download the ISOs for Citrix Xen Server.
There are two ISOs, one is the Citrix Xen Server and the second one is the Linux Guest support. I suggest you to donwload both and burn them in CDs. The Linux Guest support contains some addtional templates that they are good to have.
Boot the machine with the Citrix Xen Server CD and follow instructions.
Only configure one NIC with you management IP.
In addition, do not forget to download XenCenter on your windows desktop and install it.
After XenCenter installation, you can set the management ip and access Citrix Xen Server Remotely.
If you want to add another server, follow the installation procedure and then add it to XenCenter.
In XenCenter, you can configure everything else you need. I recommend you to configure the other NICs. If you only have one more and you want to enable VLANs, do so on the switch and then create the sub interfaces on XenCenter for each VLAN. If you want to create a pool, remember that all the server you have the same configuration or access on the network.
After the pool is created everything will be set up for the pool and no just for that server.
For installing new VMs, I suggest you to use NFS or CIFS to maintain the ISOs. You just have to add that storage on the storage tab on XenCenter and all the ISOs will be available to all VMs.
You can create machines with any OS however Citrix Xen will tell you that they only support the ones that they have templates for. So try to use the templates for the creation and then boot the VM with the ISO for that template. The template will guarantee that the VMs is compatible with Xentools, however this package is not required by the machine to operate.
Finally , set up the shared storage. Shared Storage will give you the flexibility to move the machine from one server to another one (XenMotion) without losing service or network. A normal set up will include some class of ISCSI target ( Shared Storage) which can be accessible by Citrix Xen Servers.
I recommend you to check any of the Opensource SAN (Openfiler, Freenas) solutions or if you have the budget go for Commercial solutions.