Word – How to print in black & white?

You could use HTML instead of word documents.

Not only is it a standard and easily viewed, but you can actually define different stylesheet for screen and printer.

Depending on your needs, you can knit the markup by hand or customize TinyMCE for your needs.
Or, as is quite common, you could use a wiki system to write your documentation, which would also give you all the features of a wiki (versioning, linking, searching, tagging etc.).

Try removing the margins from your document. Currently it says 'Normal Margins' in your print settings. Try setting the value to custom and then set zero margins. If that doesn't work you can create a new paper type called 'Borderless' with custom size and margin, so that Word does not try to impose A4 specification to the printer driver.