That might not be possible.
Typically when netbooting a small image gets downloaded through tftp (that contains network drivers and and a very basic operating system) and then it will connect to a network drive that contains the rest of the files needed to boot.
Because of the file size limitations of TFTP, and the fact that the ISO needs to be stored somewhere while the computer boots - you can't just boot an ISO over the network.
What are you trying to boot over the network? If it's linux you may want to take a look at the linux terminal server project. It's a great way to learn about tftp and the like. If it's windows, the windows automated install kit is another cool project to learn.