If you want to know what to do in each port please go to this site that I direct every one to - Try google and 'cruise ports call boards' - click on the the first result will give you all the info under the appropriate ports section on the page under Europe
Yes if you google maps Casablanca you will see the port gates are at the bottom of the street that leads straight up to the medina (old town market) & main shopping areas. 10 minutes walk.
Mr Hallett - I suspect that you have had a price drop on your cruise - get onto your T/A and get them to give you the cheaper price - about £50pp cheaper at the mo.....
Yes it is possible to walk it but be prepared to be hassled by all the taxi drivers at the port gates who are very persistant.