Logitech Media Server development on Windows
Getting Started on SlimServer Development on Windows
(This doesn't have all the answers, or even close, but it might get you past some of the obvious stumbling points.)
The sources that are included with the SlimServer distribution pretty much aren't used under Windows. (Just to confuse things, some of them are used.) Most of the Perl code is compiled into slim.exe.
You must download and install ActivePerl (free).
Once you've made changes to the Perl sources, you run your modified server by saying
C:\Program Files\SlimServer\server> perl slimserver.pl
You cannot control your modified server using slimtray. You can stop it by typing ^C. There is another way to control it, running it as a Windows service, but I don't know how.
You might want to retrieve the official source distribution using Subversion, which you can get from here. You probably want this file. You don't need to do this if you are just hacking around, but you do need to if you want to contribute your changes back.
Well, I know that doesn't tell you everything you need to know, but at least maybe you won't be stumbling around in the dark like I was.