I installed Kubuntu on a computer for my Brother. While it works well for a desktop it is a bit bloated for a server. Could it work? Sure, I would think so. Would other distros work better? Most likely.
If you are experienced with Linux, you way want to try Gentoo. It is not noobie friendly but if you know your way around commands and are willing to give it a try, it is amazingly fast. You also get to customize just about every setting there is. It is not binary based tho which means you have to compile everything. Fast CPUs and healthy amounts of memory are a good idea. Very good cooling is a must have. You don't need any GUI to run Gentoo. The install and most updates are done in a console or text based, like the old DOS days.
Another distro that I know used to have a servers setting during the install was Mandriva. I have not used it for a good while so I don't know how bloated it is. I do know it is binary based so no compiling or very little compiling would be needed. This may be a good option if you have a slower/older machine, limited memory etc. It may also be good if you are somewhat new to Linux since a lot of it is GUI based.
You may also want to check into distrowatch. It list about all the distros and some information about each.
Hope that helps.
