Two not mentioned already:
From Stone to Steel - a truly excellent though out of print book on weapons and armour, from Monkey God - has very simple optional rules for this, but doesn't really cover any of the 'knock-on effects', other than to casually suggest that a Base Defence bonus to AC might be appropriate, if one so wishes.
Conan OGL (from Mongoose Publishing) has Armour as DR by default, as well as Parry and Dodge scores, and uses some quite innovative methods to get around the otherwise inevitable consequences to the core system. Weapons have different AP (Armour Piercing) values to which an attacker's Str bonus might be added, and if this total equals the suit - or assortment - of armour's total DR, then that DR is halved for the purposes of that attack. Also, Finesse fighting works differently - much more like D&D combat, in fact: the defender's armour's DR effectively becomes AC, and the attacker gets to add their Dex to their finesse weapon's AP value.. and if they succeed at overcoming armour this way, the 'DR' is ignored entirely for that attack.
Of course, Conan's a setting first and foremost. But the system still has some other things to offer, such as magic that better suits that kind of world.
Anyway, the most simple immediate way of getting access to Armour as DR rules to have a look at and maybe try out is, as someone already posted above, via
http://d20srd.org. Or yeah, picking up UA. Note: even UA doesn't cover many of the consequences that will arise by bringing in these rules. It requires a better subsystem as a starting point, or a bit of house ruling, IMO.