You can re-allocate you voluntary skill (the fighter/ranger/mage choice at the start), but not your slayer skills, you will always have your starting slayer skills after a respec - e.g. you will always be able to mindread in the game.
I think + magic damage is better than + physical damage on weapons because +magic also stacks with your damage spells (assuming you use damage spells). Raze is right about dual-wielding. If you have +100 damage on both weapons, then both weapons will get both bonuses (e.g. +200/weaon, +400 in total).
If you want the ultimate melee combatant later in the game, use some malachite gems to enchant both enchants (+100 magic damage and +100 physical damage) on both weapons, you'll basically be getting +800 damage, assuming you have enough dual-wield skill to avoid penalties on the off-hand damage. +Magic and +Physical damage are considered to be separate enchants, so you can put both on a single weapon.
If you're a pure caster, just put +100 magic damage on each weapon (and no points into dual-wield skill) and you'll get a handy +200 damage on your spells, incuding EACH magic missile (off hand penalties do not affect the spell damage bonus).