Just FYI, in the context of a training plan, cross training usually refers to some type of cardio activity that will give you the benefits of an elevated heart rate without the wear on your legs. However, strength training in conjunction with running for marathon training is always a good idea. My suggestion would be to keep it limited to 2-3 days per week, nothing too heavy (body weight or light weights to avoid excessive fatigue on your legs) and really focus on your core strength and maintaining flexibility. A strong core and flexible muscles will definitely help to minimize your risk of injury.

I do a mixed gym session, so cross trainer / elliptical (20 mins), stepper (10 mins), rower (10 mins), bike (10 mins) and a fast mile on the treadmill (I run slow normally), then a do a quick weights run through (not proper weights - the fixed machines) as my cross train day.

I was supposed to run today but slightly overdid sunday, then slightly overdid Tuesday so did a cross train tonight instead to give my poor thighs a rest..