Well, the simplest way would be to do a glTranslate just before you draw the background. You're already pushing the matrix to save it, which means the translate won't affect the rest of your code. You only need to push/pop once. All pushing and popping does is save the current matrix for you; flags like GL_BLEND are handled separately. So, suggestion:
Just change the someYOffset every frame, left or right, and you'll have a scrolling background.
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); // blending on a background texture? is that really necessary?
glBindTexture(GL_TEXTURE_2D, BackgroundTexture[imageNumber].texID );
glTranslatef(someYOffset, 0.0f, 0.0f);
int height = 100 * 1.333/1.5; // you're not using this variable anywhere...
glTexCoord2i(0,0); glVertex2i(0,600); // you can use the i variants if you're passing integers