When attempting to install Windows Server 2008 R2 under XEN, after loading from the disc, the installer will blue screen with the error:

STOP: 0x0000005D (<4 hex values, last 3 being 0x0000000000000000>)

To resolve this, try to enable pae in your XEN configuration file. ie, add the following line:

pae = 1

I am currently using the following configuration under XEN 3.12. Hopefully this will help.

kernel = '/usr/lib/xen/boot/hvmloader'
builder = 'hvm'
device_model = '/usr/lib64/xen/bin/qemu-dm'
maxmem = 4096
memory = 1024
vcpus=1
pae = 1
acpi=1
apic=1

name = "xenwin"

vif = [ 'type=ioemu' ]

disk = [ 'phy:/dev/VolGroup00/winserv08r2_disk,ioemu:hda,w',
         'file:/vm/iso/win2008server-r2.iso,ioemu:hdc:cdrom,r' ]

# Boot from the CD 
boot='d'

vnc=1
vncconsole=1
vncpasswd=''
sdl=0

stdvga=0 
serial='pty'
ne2000 = '0'
usbdevice='tablet'

on_poweroff = 'destroy'
on_reboot   = 'restart'
on_crash    = 'restart'