You can use iPXE to boot into the XenServer installer via HTTP:

• Create a directory on your web server to contain the installation files (e.g. /var/www/boot/xenserver).

• Copy the contents of the XenServer installation CD-ROM to this directory.

• Decompress the files xen.gz and vmlinuz:

    zcat /var/www/boot/xenserver/boot/xen.gz > /var/www/boot/xenserver/boot/xen
    zcat /var/www/boot/xenserver/boot/vmlinuz > /var/www/boot/xenserver/boot/vmlinux

• Create an iPXE script file (/var/www/boot/xenserver/xen.ipxe) containing:

    #!ipxe
    kernel boot/xen dom0_max_vcpus=1-2 dom0_mem=max:752M com1=115200,8n1 console=com1,vga
    module boot/vmlinux xencons=hvc console=hvc0 console=tty0
    module install.img
    boot

• Instruct iPXE to boot from your xen.ipxe script, e.g. using

  chain http://your.web.server/boot/xenserver/xen.ipxe

• These instructions are based on the XenServer PXE documentation.