Windows Server 2003 was released April 24, 2003 and comes in three different flavors: Standard, Web and Enterprise. These screenshots are of the standard version.
Server 2003 is basically Windows XP, with a slightly updated kernel (NT 5.2 instead of 5.1), server-specific management features, all the extra useless applications ripped out, and without the stupid themes.

The Server 2003 setup is very similar to XP, except it's colored grey instead of blue for some reason (dull theme for a dull working environment?). It still manages to get the install time remaining wrong every time, just like XP.

The splash screen is also grey, unlike XP's blue (or green for earlier versions of XP Home Edition).

If you accidentally knock the server off a shelf and it shuts off (or Windows crashes for the 847294832749583th time), you are required to provide reasoning as to why. This is part of the stricter nature of Server 2003 when compared to XP and even older server products.

Rather annoyingly, Server 2003 includes that useless product activation feature. Some versions don't appear to have it however.
I'm not quite sure what purpose activation has in a server environment, all it really does is make it practically impossible to do unattended installations and serve to annoy system administrators.

Another thing Server 2003 bugs you about on first boot is the installation of updates. I'm not positive, but I'm pretty sure Server 2003 uses the same update framework as XP.