Please read your manuals or at least the MAX FAQ that I post
here every Monday. It's all in there. But... as I'm such a
nice guy I'll give you a hint; Open the Material Editor and
open the Maps rollout. Klick on the Diffuse button and select
Bitmap from the "Material/Map Browser". Now in the Material
Editor there is a button next to "Bitmap:". Click it and
you will have a browser window where you can select whatever
bitmap you want from your filesystem.
Kind regards,
/Stefan Jansson