The GP2X, Wiz and Pandora don't have a device context in the same manner as Windows does, so GetDC doesn't exist, and neither does SetPixel unless you write it yourself (or use a library in which someone has written it for you).
Assuming you are going to use SDL, then the equivalent code might look like:
Uint32 *pixmem32;
Uint32 colour;
colour = SDL_MapRGB( screen->format, r, g, b );
pixmem32 = (Uint32*) screen->pixels + y + x;
*pixmem32 = colour;
Where r,g,b are the rgb of the color, and x and y are both offsets (with y suitably multiplied depending on the horizontal resolution).