Much as lord-fu said, many distributions are "marketed" for a particular environment, or type of user. Slackware, for example, is generally geared toward those who want to get down-and-dirty in the command-line, with few wizards or built-in help prompts. It was perfect for me, and I love how minimalistic I can make it, which makes it quite good for servers, but that type of setup isn't fitting for many people.
The difference between "Workstation," "Desktop," and "Server" is largely a matter of use -- a Desktop is traditionally a box that wouldn't be used for work, a Workstation a box primarily used for office-related applications, and a Server is a machine that is connected to by other computers, and generally doesn't have a need for direct KVM input (keyboard, video, mouse). All of these are defined by the applications and services installed. The kernel itself doesn't change much, other than offering SMP (multiple-processor) support if needed; I use the same kernel (albeit with different modules) on four different machines -- a desktop, a workstation, and two servers.
Take a look around and you will find many many many many many threads on choosing the right distribution, as well as many forums for specific distros -- I'm sure you can find one that will both suit your needs and suit your computer usage style.
Last edited by Poetics; 09-26-2007 at 01:35 PM.