Cursed swords aren't meant to be used by zombies.
There aren't really any guidelines for how to handle this.
If you're a player and trying to get a zombie enemy to pick it up I would (as a GM) just say that the sword has no effect on them. If you're a GM, why would bother giving the zombie a cursed sword?
Can Zombies use swords? I thought the only attack they had was Slam.
Well, remember that they get a save to avoid the affect of variant channels.
Variant channeling has the same area of effect, save DCs, uses per day, and other rules relating to channeling energy. Feats and abilities that modify or present alternative uses for channeled energy (such as Command Undead and Turn Undead) work normally with these variant channeling abilities.
Just keep in mind, if you do this your players will hate you. No one likes being forced to use a s$@%ty weapon because they failed one saving throw and succeeded on a combat maneuver. Cursed weapons can last a long time unless your PCs have remove curse.
Also, if the zombies are wielding the weapons this wont work. The steal combat maneuver is used to steal an item off of the character, disarm is used to disarm a creature of a weapon it is currently wielding. Also, characters would get to decide what item they get to steal off the enemy. They could attempt to steal anything on the zombie, not just a weapon on their belt.
Also, do keep in mind that unless your PCs have Improved Steal they will provoke an Attack of Opportunity from the zombies, and any damage they take applies as a negative modifier on their combat maneuver check.
You can attempt to take an item from a foe as a standard action. This maneuver can be used in melee to take any item that is neither held nor hidden in a bag or pack. You must have at least one hand free (holding nothing) to attempt this maneuver. You must select the item to be taken before the check is made. Items that are simply tucked into a belt or loosely attached (such as brooches or necklaces) are the easiest to take. Items fastened to a foe (such as cloaks, sheathed weapons, or pouches) are more difficult to take, and give the opponent a +5 bonus (or greater) to his CMD. Items that are closely worn (such as armor, backpacks, boots, clothing, or rings) cannot be taken with this maneuver. Items held in the hands (such as wielded weapons or wands) also cannot be taken with the steal maneuver—you must use the disarm combat maneuver instead. The GM is the final arbiter of what items can be taken. If you do not have the Improved Steal feat or a similar ability, attempting to steal an object provokes an attack of opportunity from the target of your maneuver.
Also, your GM shouldn't let you intentionally make cursed items if you are a player.
There really isn't a guideline as to whether cursed items apply to mindless undead.
As a GM, I would certainly say that it applies to sentient undead, despite being normally immune to mind affecting effects the item is "cursed". For mindless undead, I would have a hard time saying it should apply to them. Or that they would even be capable of using it. Honestly, I think someone else would have to put it on their belt, but in doing so would be subject to the curse.
I'm glad the information I have provided has been useful to you.
