The numeric values given below are taken directly from the Serpent Isle hintbook, Balancing the Scales. 

Other values than those given are not known to the author of this page. Sorry.


Armour and Protection

Defence Value is the number of points of damage removed from a successful attack by the armour type in question. 

Armour           Defence Value         Armour           Defence Value 
Antique Armour     2                   Leather Helm       1
Brass Shield       3                   Leather Leggings   1
Buckler            1                   Magic Armour       5
Chain Armour       3                   Magic Gauntlets    3
Chain Coif         2                   Magic Helm         4
Chain Leggings     2                   Magic Leggings     4
Cloak              1                   Magic Shield       4
Crested Helm       2                   Monitor Shield     2
Curved Heater      2                   Plate Armour       4
Decorative Shield  3                   Plate Leggings     3
Door Shield        3                   Scale Armour       2
Dupre's Shield     4                   Serpent Armour     6
Gauntlets          2                   Serpent Earring    1
Great Helm         3                   Spiked Shield      3
Kidney Belt        1                   Stocking           1
Leather Armour     1                   Sword of Defence   3
Leather Boots      1                   White Breastplate  4
Leather Gloves     1                   Wooden Shield      2
 

Weapons Fair and Foul

Damage is the amount of injury inflicted by a successful attack with the weapon, while range is approximately one pace
                                 times the value given for that weapon.

Weapon             Damage Range          Weapon            Damage Range
Arrow                 +1     -           Pitchfork            2     2
(Added to Bow Damage) 
Arrow, Burst          +2     -           Powder Keg           40    16
(Added to Bow Damage)                    (Explosive)                                        
Arrow, Magic          +4     -           Rake                 2     2
(Added to Bow Damage)                     
Arrow, Serpent        +1     -           Scythe               7     2
(Added to Bow Damage)
Axe, two handed       7      4           Serpent Dagger       2     2
Axe, Magic            8      16          Serpent Scepter      5     2
(Can be Thrown)                                                         
Blowgun               3      6           Serpent Staff        8     2
Bolt                  +0     -           Serpent Sword        6     2
(added to Crossbow Damage)                                                     
Bolt, Magic           +2     -           Shears               1     2
(added to Crossbow Damage)                                                                              
Boomerang             3      8           Shovel               6     2
Bow                   6      10          Sling, Magic         3     8
                                         (Doesn't use ammo)   
Bow, Infinity         6      14          Spear                6     2
(Doesn't use ammo)                       (Can be Thrown)                                            
Bow, Magic            12     16          Spiked Shield        2     2
Cleaver               2      2           Staff                6     3
Club                  3      2           Staff, Blue Firedoom 20    10
Crossbow              10     13          Sword                6     2
Dagger                1      2           Sword, Decorative    4     2
Dragonslayer          7      2           Sword, Fire          8     2
Fire Wand             10     8           Sword, Glass         127   2
                                         (One use only)
Fishing Rod           1      3           Sword, Magic         7     2
Halberd               10     3           Sword, Two-handed    8     4
Hammer                4      2           Sword, Wooden        2     2
Hammer of Dedication  8      2           Sword of Defense     6     2
(Can be Thrown)                                                                       
Hammer, Juggernaut    25     16          Throwing Axe         4     2
(Can be Thrown)              
Hammer, Twohanded     9      3           Tongs                6     2
Hammer, Worm          6      2           Torch                3     2
Hoe                   2      3           Torch, Lit           6     2
Mace                  5      2           Whip                 6     3
Magebane              9      2           Whip, Lightning      10    3
(Neutralizes target's magic)                                    
Morningstar           5      2           Zot Wand             8     8
                                         (Fires Poison missiles)
Pick                  4      2
                                           

Note that the Zot Wand does not seem to have been implemented within the game.
Erinon's Axe (Silver Seed) has Damage 20, Reach 4. 
Also this list is incomplete, but it is all that is listed in the manual. Further values (the Black Sword in particular) are unknown.