On some machines, fullscreen video surfaces with the same width and height are shown rotated by 90 degrees to the left.
The following simple test program, which is supposed to draw a horizontal line, shows this problem on the HP Compaq dc7600 Convertible Minitower (Intel Pentium 4 at 3.2 GHz, Intel 82945G Express Chipset Family):

***

#include <windows.h>
#include "SDL/SDL.h"


#define WIDTH 480
#define HEIGHT 480
#define DEPTH 32


int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
	if (SDL_Init(SDL_INIT_VIDEO|SDL_INIT_TIMER) != -1)
	{
		SDL_Surface* w;
		Uint32* r;
		int x;

		w = SDL_SetVideoMode(WIDTH, HEIGHT, DEPTH, SDL_SWSURFACE | SDL_FULLSCREEN);
		
		SDL_LockSurface(w);
		r = w->pixels + w->pitch * HEIGHT / 2;
		for (x = 0; x < WIDTH; ++x) r[x] = 0xFFFFFFFF;
		SDL_UnlockSurface(w);
		SDL_UpdateRect(w, 0, 0, 0, 0);

		SDL_Delay(1000);
		SDL_Quit();
	}

	return 0;
}

***

A few additional notes:

 - using anything greater than 481 for WIDTH allows the display to be set up correctly;
 - the very same binary works perfectly on other machines;
 - a few friends, trying the game demo available at http://saimobvq.interfree.it/uniVERSUS/index.html, also reported different/worse problems, the worst of which being the impossibility of opening the video surface altogether (on a Sony Vaio - sorry, I have no other information about that machine);
 - SDL 1.2.9 worked just fine (don't know about 1.2.10 as I directly jumped to 1.2.11);
 - all the programs ever tried were compiled with MinGW.