What tool would be best to create an access plan (with directions written on roads, local zooms, etc.) from OpenStreetMap (preferably using the MapQuest Open map)?
Grab the images from the web client of whatever map provider you want, then add annotations using a graphics package.
All you need is a screen grab app and Inkscape, if you've not got a license for adobe illustrator..
Make sure you don't violate the terms of service if your map data provider.