Article : Ubuntu PXE Boot

Mount ubuntu live iso on pxe server
mkdir /mnt/iso
mount ubuntu-10.04-desktop-i386.iso /mnt/iso

Create nfs share for ubuntu & copy all the content of live cd to it
mkdir /nfs-share/ubuntu -p
cp -rfva /mnt/iso/* /nfs-share/ubuntu/
cp -rfva /mnt/iso/.disk /nfs-share/ubuntu/

Enter following in /etc/exports
/nfs-share/ubuntu/ *(no_root_squash,rw,async)

Apply changes
exportfs -rv

Enter following in /tftpboot/pxelinux.cfg/default

LABEL Ubuntu-10.04
kernel /tftpboot/images/ubuntu/vmlinuz
append boot=casper netboot=nfs nfsroot=NFSSERVER:/nfs-share/ubuntu initrd=/tftpboot/images/ubuntu/initrd.lz

Copy initrd and vmlinuz from Ubuntu live cd to tftpboot
cd /nfs-share/ubuntu/casper
cp vmlinuz initrd.lz /tftpboot/images/ubuntu/