Ok, I'll bite. Got nothing better to do anyway, and sometimes feeding the troll can actually be a bit of fun (which is my sole intention here).
So; instead of biting the hand that fed us why didn't you come up with some requirement analysis? Anyone can say they don't agree, these days very few seem capable of providing some motivation.
Thing here is that it doesn't really need much of an analysis because Windows Server 2k3, which IMO is a very impressive piece of work, still suffers from quite severe limitations. And that makes its overall functionality limited. Example; Microsoft pulled it off by making PowerShell (actually this is the management framework) not only available for the products it was designed for (Server 2k8 and up, and Windows 7 and up) but also "down ported it" (as I like to call it, I know it's not entirely right). Meaning? I can administer my in-house 2k3 servers using PowerShell on my Windows 7 client. I don't care what others think, but in my opinion it's a pretty impressive display (it helps that PowerShell is my favourite administrative tool on Windows of course).
But that awesomeness is still overshadowed with other limitations. IPv6 for example? You're better off not using this, because although it provides some basic support for it, how safe will you be if you're using a firewall which only supports IPv4?
And of course this is not even addressing the very obvious: what roles does 2k3 actually provide? Far less than 2k8, that's for sure:
- File server
- Application server
- DNS server
- DHCP server
- WINS server
- Print server
- File server
- Mail server (POP3 / SMTP, no IMAP)
- Terminal server
- RAS / VPN server
- AD domain controller
- Streaming media server
Rest assured that your average Linux or *BSD environment has everything it needs which might be required to take over these roles. Including tasks such as WINS or (limited?) AD thanks to the existence of the Samba project.
Even if your environment is using SharePoint (which my server is doing; used as a test environment. One which, once again, is administered through PowerShell) then you might still be able to pull this off. Because although the Mono project doesn't support the latest in .NET technology (talking .NET 4.5 now) neither does server 2k3. The best you'll probably manage is .NET 3.5. This is what I'm currently working at; testing how hard it'll be to move some projects over onto a FreeBSD / Mono environment. So far the results are looking quite good. Even Visual Studio (2012) has no problem at all with compiling and distributing website projects onto a FreeBSD powered server.
So yeah, if you don't got Christian's message above then it's most likely because you hardly understand how this 2k3 thing actually works. But here you got something which spells it all out for you ;)