I just installed the new Release Candidate for Windows Server 2003 Service Pack 1. Superfically, it appears to have most of the security features from Windows XP Service Pack 2. So far no problems with the install or interaction with anything I previous had running.
I use Windows Server 2003 as my main workstation. I do this for many reasons which I won't go into here. One thing I have found out is that 128MB of memory simply isn't enough. On a 2.4Ghz Dell PowerEdge server with 128MB of memory, the system is pretty slow with a couple of Microsoft Office applications (like Outlook and PowerPoint). I just put in 256MB of memory and responsiveness is much better.
I did configure most of the advanced settings to change priorities to boost foreground services and other performance tweaks.
I'm going to get 1GB of memory shortly, but I wanted anyone else who's thinking of running W2K3 as a workstation to know that 256MB is neccessary for productivity. Here's another link if you're considering using W2K3 as your main workstation.