On Windows there is the regular [aka non-SDL] build. Why not try building that one? It doesn't need libsdl.
One thing you can do on Windows, start a command prompt [cmd.exe obvious] and navigate to the DarkPlaces source folder. Type "make" and then the DarkPlaces script asks you what to build and then select one of the options that doesn't have "SDL" in the name.
That being said, if you are using DarkPlaces you don't really need engine modification as the engine is designed to do most of the stuff that requires engine modification via a myriad of other methods.