Bitmap Texturing versus Drawing.

Hey folks, I am still new to game programming and I am considering writing a space invaders clone. I was wondering if, to display the invaders, if I should try to draw them using graphic routines, or if I should just texture a quad with a bitmapped image. The second one sounds resonable to me, but I am not the one with all of the experience and expert opinions. Also, I use OpenGL right now, if that helps responses. Also, I read nehe''s texture mapping tutorial, and was wondering why he put such restrictions on the bitmaps that are used. How hard is it to deal with images that don''t fit these restraints? Thanks in advance.