Great, we need to add a new server to the pool of Citrix Xen and we do not want to use the CD.
Follow these instructions an you can install Citrxi Xen using a USB drive.
After installed you can join the server to the pool, however you have to make sure that the Linux pack has been installed.
You will receive a message saying different version so the server can not be added it.
If you do not have the linux pack installed , create a USB drive with the Linux Pack ISO, then plug in it to the server.
#mount /dev/sdX1 /mnt
Make sure what /dev/sdX the server assigned to the USB. (you can check that using dmesg)
Done, now you can join the server to the pool.