To receive the benefit of a shield's enchantment (resist magic, for example) does my character actually need to have it equipped? or just in their inventory?

You need to have it equipped to receive the benefits, just like with all other enchanted equipment.

You have to have it equipped to recieve any benefits from it.

I know what you are saying.
I use a bow AND a sword and shield, so when I go from my bow to my sword, my shield is automatically equipped and brought out.
I would think though that you would have to have it equipped and out for it to be taken into effect.
The best way to check this would be to check the "active effects" section under Magic.
Or
You could look at your armor rating when your shield is def equpiied and also when your shield is sheathed.

thx. figured as much. I am trying to stack RESIST MAGIC apparel, but I don't want this shield ...yet, I'll need it to achieve the 85% I think.