I have looked around and I seem to find different answers everywhere. If I equip a shiled my armor rating goes up as soon as I just equip it. But does this mean I can take more damage when I just walk around with the shield not even raised?

Yes. (unless you have reached the armor cap without the shield)

Now, by actually Blocking, you will of course reduce even more incoming damage.

Hm that svcks a bit :/ There is no mod out there that only makes the shield effective against spells and hits if they actually hit the shield?

This.

The armor cap, with 4 pieces of armor equipped is 567.

Spellbreaker from the Daedric Quest.

Why does that svck?

The Elemental Protection perk only works against spells that hit the shield.

For combat you could look at a mod like http://skyrim.nexusmods.com/mods/2700

Actually it protects you no matter the direction of the incoming spell. It could hit you in the back and still be just as effective.

As long as you have the shield raised.

Ok - I was going by the information on UESP.

And some claim it http://elderscrolls.wikia.com/wiki/Talk:Elemental_Protection

Only works in Oblivion. Magical shield can be equipped and offers protection while you two-hand or bow it.

I mean it svcks that you get armor just by running around with the shield. That does not make much sense... But how do the shield work against magic? What if a shield have an armor rating of 50, will that help anything against lets say a dragon spraying you with fire?
Or how does it work if the shield have an enchantment to protect 50% against fire. Will that always be "on" even though you are not even raising the shield? Or will it boost your defence against fire in the same way if you actively block melee damage with it?

Exactly.

That link is not the UESP. The Wiki is not as reliable as the UESP. That guy didn't think the perk worked at all. chances are, he didn't have his shield raised.

The UESP ...

Great Blocking vid...http://www.youtube.com/watch?v=DOKgNkufZAI

Damn! I even triple posted...

Any enchantment that is added to your apparel, like resist fire, will be associated directly to your character. That has nothing to do with suppressing fire with the shield. It's no different than enchanting boots with 50% Resist Fire.

Yeah, I think the OP is missing the point that the shield is rather unique in that it is both a passive piece of armor (like boots or gauntlets) and potentially an active piece like a weapon. Even when it's not actively being wielded, it's still a hunk of metal or armor-like material covering prime body real estate (upper thigh, hip, part of the abdomen) -- compare it's geography, if you will, to the passive coverage of boots and the liklihood that its real estate will be targeted.

Generally, a shield's passive AR is equal to that of the equivalent material AR of boots + gauntlets, which makes sense when you consider the liklihood of the areas it covers being hit vs. the ones they cover.

Now if you actively use the shield to block, of course, you're really using it as much as a weapon and less as a defensive covering. You're now using it to parry, push back, create openings, cause imbalance, etc. And keep in mind that none of Block Perks are effective unless the shield is raised and, thus, one is actively using the shield.

or svck it