Is a longsword with an enhancement bonus considered magical and able to hit incorpreal creatures?
If it is a +1 or greater weapon it is considered magical and can hit incorporeal. If it is a Masterwork Weapon only, then it cannot.
Incorporeal
Creatures with the incorporeal condition do not have a physical body. Incorporeal creatures are immune to all nonmagical attack forms. Incorporeal creatures take half damage (50%) from magic weapons, spells, spell-like effects, and supernatural effects. Incorporeal creatures take full damage from other incorporeal creatures and effects, as well as all force effects. See here for additional information.
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Incorporeal (Ex)
An incorporeal creature has no physical body. It can be harmed only by other incorporeal creatures, magic weapons or creatures that strike as magic weapons, and spells, spell-like abilities, or supernatural abilities. It is immune to all nonmagical attack forms. Even when hit by spells or magic weapons, it takes only half damage from a corporeal source (except for channel energy). Although it is not a magical attack, holy water can affect incorporeal undead. Corporeal spells and effects that do not cause damage only have a 50% chance of affecting an incorporeal creature. Force spells and effects, such as from a magic missile, affect an incorporeal creature normally.
An incorporeal creature has no natural armor bonus but has a deflection bonus equal to its Charisma bonus (always at least +1, even if the creature’s Charisma score does not normally provide a bonus).
An incorporeal creature can enter or pass through solid objects, but must remain adjacent to the object’s exterior, and so cannot pass entirely through an object whose space is larger than its own. It can sense the presence of creatures or objects within a square adjacent to its current location, but enemies have total concealment (50% miss chance) from an incorporeal creature that is inside an object. In order to see beyond the object it is in and attack normally, the incorporeal creature must emerge. An incorporeal creature inside an object has total cover, but when it attacks a creature outside the object it only has cover, so a creature outside with a readied action could strike at it as it attacks. An incorporeal creature cannot pass through a force effect.
An incorporeal creature’s attacks pass through (ignore) natural armor, armor, and shields, although deflection bonuses and force effects (such as mage armor) work normally against it. Incorporeal creatures pass through and operate in water as easily as they do in air. Incorporeal creatures cannot fall or take falling damage. Incorporeal creatures cannot make trip or grapple attacks, nor can they be tripped or grappled. In fact, they cannot take any physical action that would move or manipulate an opponent or its equipment, nor are they subject to such actions. Incorporeal creatures have no weight and do not set off traps that are triggered by weight.
An incorporeal creature moves silently and cannot be heard with Perception checks if it doesn’t wish to be. It has no Strength score, so its Dexterity modifier applies to its melee attacks, ranged attacks, and CMB. Nonvisual senses, such as scent and blindsight, are either ineffective or only partly effective with regard to incorporeal creatures. Incorporeal creatures have an innate sense of direction and can move at full speed even when they cannot see.
Format: incorporeal; Location: Defensive Abilities.
You may find it useful to carry a backup weapon:
Price 5 gp
Type simple
Named for the common aspergillum, a macelike tool used by priests to sprinkle holy water, this light mace has a hollow head and a metal plug closing off the hole through which the head is filled. When the mace strikes a creature, holy water sprinkles out through tiny holes throughout the weapon's head; creatures subject to damage from holy water take 1 point of damage in addition to the normal effect of being struck by the mace (a nonmagical aspergillum can deal holy water damage to an incorporeal creature in this manner, even if the mace itself deals no damage). After 5 hits, the battle aspergillum is empty and needs to be refilled. Filling it with holy water is a standard action that provokes attacks of opportunity (like drinking a potion). A filled aspergillum is normally carried upright, to prevent the holy water from leaking out as the weapon moves.
(emphasis mine)