Netboot Ubuntu 12.04 (32-bit) from ftp.ntua.gr using iPXE (taken from gist.github.com/2234639.git)

ubuntu.ipxe

#!ipxe

# Set server where image will be downloaded.
# archive.ubuntu.com works fine but you can use your own.
set server archive.ubuntu.com

# Specify a distro
# Just type the distro codename here...
set distro quantal

#32/64 menu
menu Ubuntu (${distro}) 
item 32 32-bit
item 64 64-bit
choose version
goto ${version}

:32
echo Loading Ubuntu ${distro} (32-bit)...
set 209:string pxelinux.cfg/default
set 210:string http://${server}/ubuntu/dists/${distro}/main/installer-i386/current/images/netboot/
chain ${210:string}pxelinux.0

:64
echo Loading Ubuntu ${distro} (64-bit)...
set 209:string pxelinux.cfg/default
set 210:string http://${server}/ubuntu/dists/${distro}/main/installer-amd64/current/images/netboot/
chain ${210:string}pxelinux.0