Stayed there last Feb, and I would find it difficult to stay at this resort without a car, unless I was planning to hang out by the pool most of the time. The problem is that the resort is not in Marbella, but about 10 km outside of the town just off a busy freeway (A-7)
Bus service is about a 5 minute walk away.
There is a small strip mall (Contour) with a small supermarket and few resturants with about 1-2km away. On the other side of the freeway there is larger cluster of resturants with a SuperSol, closer to 2+ km away. Bus service is about a 5 minute walk from the resort.
The resort does offer bus tours to some of the nearby sites.
And the cost to rent a car from the resort for a day, was almost as much as what we paid to rent a car for a week from the airport. I think when you add in the cost of transport from the airport and back, even if you rented a car and just let it sit, you might be better off.
Here is a link to Google Maps for where the resort is:
http://maps.google.com/maps?f=q&hl=en&geocode=&q=Calle+de+C%C3%A1diz,+29601,+Marbella,+Malaga,+Andalusia,+Spain&sll=36.507394,-4.856987&sspn=0.003855,0.006866&ie=UTF8&t=h&ll=36.489757,-4.770598&spn=0.001928,0.003433&z=18&iwloc=addr
If you zoom the map out a few times, the Contour and Supersol are labelled on the map. They are NW of the resort near the off ramps from A-7.
This is probably one the nicest resorts that I have stayed at in the Marriott system - sure you will have a great time. Hoping to go back in March, but may go to Malta instead.