I want to load a bitmap to the back_buffer and flip it to the primary. How do I?

it sounds like you want to use directX, where back buffering and flipping are built into a direct draw primary surface which has DDSCAPS_COMPLEX and DDSCAPS_FLIP capabilities. there is an article on gamedev which will guide you through this, but i haven''t got the URL, however the same article is at

http://www.geocities.com/SiliconValley/Bay/2535/ddrawtut.html

(the author''s site i guess.)
if you want to avoid direct x, or are programming in a window (complex direct x objects can only exist in full screen mode) you will have to create an HDC, blit onto this and then blit this onto the window''s HDC.