It is a successor to the Windows 2000 operating
system that can be used both as a server and as a workstation, where a conversion may be
done (although undesirable at the registry level - you essentially
get a bloated XP then) by hand, preferably. The system runs
indeed smoothly, but only if a
person knows what he is doing. The system is more picky on various drivers' defects, so one has to adjust for example the service "Start" type from Auto (2) to On demand (3). The system also accepts nearly all Windows XP drivers (the Compatibility
tab helps to the rest) so that no faux-pas seen on the Windows XP rise vs. older hardware can surprise you. You can download a Service
Pack 1 for this system and integrate it into your installation to fix many bugs and enable the NX bit-
based buffer overrun protection.
To return to the conversion to a desktop environment, I recommend tweaking in gpedit.msc a lot and copy nusrmgr.cpl from Windows XP to simplify the user management. You use the said Group Policy Editor to remove the "Press Ctrl+Alt+Delete" nag screen, remove the asking for the reason for shutdown etc.
Right now, I'm running many services and applications on my
Windows Server 2003
box. They include all of the common internet services - the web, secure HTTP, FTP, DNS, DHCP, NAT routing with port forwarding and countless small ones. As for the user interface (UI), I use StyleXP. All "serious" applications
work, I can play GTA:SA, DOOM 3, Manhunt, Postal 2 and most other such games under this OS.