I would like to know what the difference is between these two versions of the same distro.
I think that the alternative CD is not Live,
but is there any more to it?
Yes. The alternate CD comes with all the Ubuntu packages (and so can be used as an upgrade package source by simply running
The alternate CD installer is not a live CD. You can't use it to try out Ubuntu, test if Ubuntu works or fix a PC/edit partitions without reinstalling.
The alternate CD installer has a command line (curses or similar) installer, whereas the default live CD has a user friendly graphical installer.
The alternate CD can be used to upgrade your Ubuntu version. This is useful for offline computers.