The absolute simplest way to do it would be:
dbPitchCameraUp(dbMouseMoveY());
dbTurnCameraRight(dbMouseMoveX());
However, that ignores a few things, such as settings limits to how far the camera can move. While generally you'd like the player to be able to spin around endlessly, it's not a good idea for the player to be able to look up and up, until they see the world upside down. One way to limit motion would be something like this:
#define pitchUpBound 60
#define pitchDownBound -60
float cameraPitch;
while(LoopGDK()){
dbPitchCameraDown(cameraPitch);
cameraPitch+=dbMouseMoveY();
if(cameraPitch>=pitchUpBound)cameraPitch=pitchUpBound;
if(cameraPitch<=pitchDownBound)cameraPitch=pitchDownBound;
dbPitchCameraUp(cameraPitch);
dbTurnCameraRight(dbMouseMoveX());
dbSync();
}
That should work, theoretically, though I haven't tested it. 60 and -60 degrees are the assigned boundaries for up and down, though you can set them to whatever you like.
My site, for various stuff that I make.