As far as Im aware all distro's require a root password change for mysql after an installation. For something thats a piece of cake to install use Fedora Core 3 without selinux.
On all distro's you will need to configure PHP.ini to increase the memory_limit for tikiwiki and then review running services like ftp, named, etc for security points.
I would really work with a distro that I was confortable with, especially in a server environment where you might one day have to deal with repairs to the filesystem and security issues across packages.
I personally use Gentoo Linux everywhere because it allows me to perform custom compilations to optimise speed and enable special tricks for the ultimate in TikiWiki performance. There Gentoo Handbook is very easy to follow and makes the installation a breeze.
So to summarise my easy install recommendation is a Custom package installation of Fedora Core 3 and my ultimate install recommendation is a Gentoo Linux system.
Ive used SuSE on a server once, it lasted a couple of hours
Ive used Debian on servers, they lasted a month before I changed to Gentoo
Mandrake didnt get past customisation, becuase it was way too wanting to be graphical for my server requirements.