How do I install Linux over the network , using ftp, http....
Look into PXEBoot as the others have mentioned, but if you're looking to do the network installs on a larger scale and a good system to maintain all those machines (updates, installs, etc.) then take a look into XCAT (http://xcat.sourceforge.net/).
I'll recommend to you an alternative that I'm aware of if you want a Debian based linux.
FAI (Fully automatic installation) for "large" unattended installations. A little setup has to be done, but worth it. FAI uses PXEBoot with DHCP, TFTP, NFS on a debian/ubuntu system. You can customize the install for every machine in the network using a class concept. It also integrates with CFEngine (and possible with toher management tools like puppet. I didn't try it yet).
Best regards, Humber