Very tricky and need special software, operating system and configuration before you can do it.
If your question is 'can I boot windows on computer B when its installed on computer A' then the short and only answer is no. If you want to do some exploring with linux, G-PXE, Etherboot, TFTP, etc... I have some experience in setting this up on a home LAN and can recomend some guides.
Again, this won't work for windows.