Having spent some time trying to help people in the Ubuntu server forum, I find that a lot of people fail to grasp what Ubuntu really is and how the various versions relate (particularly the server and desktop version). That's understandable given how other distributions or operating systems are packaged, so I'm going to explain it here:
First, understand that Ubuntu begins with a large pool of open source software that has been packaged up conveniently and stored on repository servers, and organized by release (7.10, 8.04, 8.10, etc).
Ubuntu server vs. Ubuntu desktop vs. Kubuntu vs Xubuntu vs whateverubuntu are not different repositories. They don't come from different pools of software. They are just different combinations of software from this same big pool.
So for example, to build the desktop version, they get a basic system, the GNOME desktop, a handful of applications, and the appropriate artwork; package them up and put them in the pool. For the server, they get the basic CLI system, a server-optimized kernel, and some popular server packages (like LAMP or BIND); package them up, put them in the pool. Same for Kubuntu, Edubuntu, and the rest.
Now, all this software goes into the same pool. So if you install apache on your Ubuntu desktop, it's the same apache that you'd be installing on your Ubuntu server. No difference. Same package.
If you install the GNOME desktop on your server, it's the same GNOME desktop you get on the desktop distro. Same version, same configuration, same bits and bytes.
Which brings me to a frustrating thing I see. People download the server disc, then install it on a piece of decidedly non-server hardware, then want to install a desktop environment. YOU MIGHT AS WELL JUST INSTALL THE DESKTOP VERSION. It'll save you the headache. You can still install LAMP. You can still install DNS, LTSP, DHCP, ebox, gopher, or whatever other crazy server app you want. It's the same stuff, the only difference is the subset of pool packages that come on the disc.
So if you are one of these folks who wants to install the server version, but doesn't want the CLI (command line interface) and isn't installing on a rack-mount, dual-processor, SCSI RAID beast; just install the desktop disc and go from there. Problems solved.