Draw a new illustration for promotional leaflets/posters

We have a Word document that we'd like smartened up with a bit of proper design. In particular, we have a diagram which we'd like redrawn. The rest of the document is quite straightforward.

We need this document to be a template, so we'd like the redrawn diagram as a JPEG that we can continue to use in a Word document. We'd like it at two sizes, one large enough to fit across the width of a portrait A3 page, and one sized down to fit across the width of an A4 page.

This job is urgent and ideally we'd like to see a first draft by 12 noon on Thursday 2nd May.