As Grumpy has already said, there are no benefits by running Server 2k3, quite the opposite, I can think of a whole host of reasons as to why you wouldnt want to run server software on a desktop.
By the time you've loaded 2k3 up with all the software one typically runs on a desktop pc it will probably be more unstable than XP because its not meant to handle that.
Also games & other apps are not designed to run on an NT OS.
Networking with 2k3 is massively complicated for a beginner and if you dont know what you're doing you will just end up going round in circles for hours when all you want to do is share a folder!
Short story.... install XP Pro for a start.
Then either have a PC kept in the cupboard under the stairs and run 2k3 on it and run your own small domain and also use it as a file server etc. Or stick with a workgroup and if you still like the idea of having a server then try Windows Home Server.
But use server software as that, a Server.