Maybe it's senility, but I sure don't remember MS pushing a new Server OS quite as hard as they seem to be with Windows 2008. System Center Virtual Machine Manager 2008 Beta and the new ISA portion of Forefront Stirling both require Windows 2008. Given that Windows 2008 is brand spanking new, this surprises me. I can remember using Windows 2000 for several years after 2003's release and most everything worked just fine with it.
Ah well. I'm particularly saddened by SCVMM 2008's reluctance to embrace Server 2003. I understand part of it's mission is to support Hyper-V but that's a small piece of the entire VMM package.
gaurhoth