here is the precompiled libs and header files and a couple of examples for using SDL on the DS.
http://gpf.dcemu.co.uk/files/nds/NDSSDLlibs.rar
http://gpf.dcemu.co.uk/files/nds/NDSSDLexamples.rar

The SDL port is based off of SDL 1.2.3 so some work is need to upgrade it to the latest version, still needs sound support and filesystem support.

Here is all the source code for each library. thanks to WntrMute on #dsdev for the source to libpng and zlib

http://gpf.dcemu.co.uk/files/nds/NDSSDL.rar
http://gpf.dcemu.co.uk/files/nds/NDSSDL_image.rar
http://gpf.dcemu.co.uk/files/nds/NDSlibpng-1.2.8.rar
http://gpf.dcemu.co.uk/files/nds/NDSjpeg-6b.rar
http://gpf.dcemu.co.uk/files/nds/NDSzlib-1.2.2.rar
http://gpf.dcemu.co.uk/files/nds/NDSSDL_mixer.rar
http://gpf.dcemu.co.uk/files/nds/NDSSDL_ttf.rar
http://gpf.dcemu.co.uk/files/nds/NDSfreetype.rar
http://gpf.dcemu.co.uk/files/nds/NDSSDL_flic.rar
http://gpf.dcemu.co.uk/files/nds/NDSSDL_gfx.rar
http://gpf.dcemu.co.uk/files/nds/NDSSFont.rar

also
here is a port of SDL for the gba and a couple of examples based off the .diff file found at
http://suse.osuosl.org/people/uli/SD....2.3-gba.patch

http://gpf.dcemu.co.uk/files/nds/gbaSDL.rar