File reading and writing is like my favourite programming exercise!! Bitmaps are really easy to use ( even easier using win32 api functions but I'm talking about raw reading with your own function ) ...
I used wotsit, the files there gave me a really good insight into the way bitmaps worked and how they were structured.
Reading and writing .bmp is a frequently asked question in many programming groups on the net. Google
is your friend here
If you need any help once you get started I'll gladly help you.