I’ve heard that there is some kind of DirectX support in SDL. Is SDL
wrapping DirectX in Win32. Or does it contain wrapper functions or
somekind of DirectX implementation in other operating systems?
SDL is its own interface, designed to be platform independant. One of
the platforms that SDL has been ported to is DirectX/Win32.
Ie. The code you write can be compiled (hopefully) for the other platforms
SDL has been ported to, and will work on them with (hopefully) no modifications.
So, it is kind of wrapper functions, but on a higher level, and wrapper
functions have been writted for a few different interfaces (like X11, Beos,
DirectX). 
cya
Josh-----
Expert, n.:
Someone who comes from out of town and shows slides.