For advice on using netboot images, see the installation guide. These are generally aimed at experienced users with special requirements.
Netboot images are available for the following architectures:
Ubuntu provides backport kernels for hardware enablement on our LTS point releases, as well as matching netboot images. Below are links to the netboot images for 12.04 with each HWE kernel. For more information about backport kernels, including the support and upgrade policies for each one, please see the documentation.