Ok, you need to try this:
//Load World.h
// switch to the media directory, load our world
// and turn lighting off
SetCurrentDirectory ( "levels/TCTS1" );
dbLoadObject ( "universe.dbo", 1 );
dbSetObjectLight ( 1, 0 );
// Chance this directory here.
SetCurrentDirectory ( "../../media" );
dbLoadObject ( "L-Ninja-Static.x", 3 );
dbPositionObject ( 3, 434, 42, -517 );
//dbScaleObject ( 3, 5, 5, 5 );
// load a model for our sky
dbLoadObject ( "skybox2.x", 2 );
dbSetObjectLight ( 2, 0 );
dbSetObjectTexture ( 2, 3, 2 );
dbScaleObject ( 2, 5000, 5000, 5000 );
that should work, because the ../ signifies to go down in the folder hierarchy.
