An Increased Damage enchantment will do either melee or ranged damage depending on the weapon type, but a melee damage charm will only help with a melee weapon (see the charm's description in the inventory). I think I saved the game and tested that at some point (attacking the same strong opponent with the same bow with and without a charm added, to see if there was a significant difference in the average damage per hit), or at least thought about doing so.
I didn't use any charms with my warrior in D2:ED or ranger in DKS.
