Are there separate desktop and server versions of CentOS?

Look closer. There is a "minimal" version available: ftp://ftp.hosteurope.de/mirror/centos.org/6.0/isos/x86_64/

There are a couple ways to do this.

I think the best way is to download the default ISO image and deselect all packages to get get a minimal install, or install just the packages that you need. Instructions for this are in the CentOS FAQ at 3. Can I install CentOS 5 with just the first CD?. If you want a lightweight OS with just X window or just an Apache webserver, this method is for you.

As an alternative, CentOS provides a "Minimal" ISO. They are also supposed to provide a "LightWeightServer " ISO, but I haven't heard anything else about this LWS version.

The CentOS 6 Release Announcement says:

+++++++++++++++++++++++

Minimal Install CD

We have also created a minimal install CD, that would bring up a base machine with just enough content to have a usable platform. This CD image will be released in the next few days.

+++++++++++++++++++++++

The LightWeightServer (LWS) CD

In order to bring back the CentOS-4 Server CD style single iso image, we are creating a LWS varient of the main distro. Details for this will be posted in the next few days with release happening after the live media and the minimal cd editions.

The Minimal ISO is available on CentOS mirrors. Look for CentOS-6.0-x86_64-minimal.iso on the following mirror, for example:

http://linux.mirrors.es.net/centos/6.0/isos/x86_64/