How can I copy the screen contents directly into a buffer?

I want to copy the image I have on the screen into a buffer.
Then I want to write the contents of the buffer into a file. Is it possible to do this, and if so
how do I do it?

I think I saw how to do this somewhere on the CodeGuru web site. Did you look?

See the 'Bitmap & Palette' section.
Section titled 'Writing a window image to a BMP file'.