I'm thinking about whether or not to try out SDL as an alternative to DirectX, seems I only create 2D games, however I can't find anywhere if SDL is required to be installed on the end users computer to play a game developed in C#, using SDL for the graphics.
Does anyone know?
Assuming you're using something like:
The end-user does need to have the SDL libraries/binaries installed on their machine, however, they don't need to manually install SDL themselves. You can distribute the SDL binaries yourself as part of your own games installer.
The license for SDL itself (not SDL.NET) even allows you to "statically" link the SDL source-code right into your own source code. From the SDL Licensing FAQ:
Q: What license does SDL use?
A: SDL is freely available under the GNU LGPL license, and may be used in both free and commercial applications.Q: Can I use SDL in a commercial application?
A: Yes! If you link dynamically (via .dll's, .so's or using other dynamic linking devices) then you do not need to do anything. If you link statically (include the SDL source inside your project when you compile) you have to provide some way for your customer to relink your application with a custom version of SDL. The details are available at: http://www.libsdl.org/license.php
The absolute newbies guide to SDL.NET will give you a list of the required libraries, both from SDL.NET (the .NET "wrapper") and SDL itself.