If it's something a player gets to use, do concentration checks once a round or once every other round or something. If succesful, it targets what the player wants it to target. If not, something random. Roll d%, high it'll do the closest friendly target, low for the closest non-friendly target. If there's nothing else to target, the player themself!

If it's not something a player gets to use.. Well, I'd just have to target random things every round until it's out of targets and then I'd forget about it.

Is it a discrepincy issue (3.0 to 3.5)?

It shouldn't be, it's a recently published WOTC adventure I'm running (well basically:>). On the other hand it might be worth checking up on, editing does seem to have been rather lax recently.

Indeed.

The easy fix would either be to change Doom to an area effect or change "continually" to "at will".

I've checked it wasn't a version issue.
That's pretty much what I've been thinking. I've also looked at other similar effects, and I'm considering giving it an "aura of despair" ala Blackguard or making it bane (same spell level).

That'd work great, as well.

I guess I don't know enough about the item or your intention for its use, but...

How about it just affects whoever is touching it?

Yeah, sorry I was keeping it vague 'cos my players on on this forum too. It's an enchanted sword wielded by the "bag guy" of the adventure. The PCs may or may not get hold of it, but the cleric is unlikely to allow it to be kept, it's heavily evil.

Ah ha. Then I'd probably agree with the aura idea discussed above ... though enemies that are using a bunch of cursed items? I'll have to file that one away... ::maniacal snicker::

It's a good balancer; evil works nicely too if there's a cleric or paladin the rest of the group respects. Although we really cursed the GM who had all of his evil chaps carrying demonic items:>
Sentient items like this work nicely too, but there is the problem of PCs suddenly becoming NPCs sometimes.

One of the first enemies my players encountered was a lich that had a bunch of items that dealt Constitution damage if you wore them. It of course didn't affect him, being undead, and my players were very put out when they realized what the problem was and that they would have to pay someone to get them decursed.

You could also have it automaticall cast Doom on any target hit by the weapon. I think the Blackguard aura might be better, but I throw it out as an option. Or change it to the Bane spell (level 1 cleric just like Doom).

I have to wonder if it's a mistake, and they'd intended the power to be "bane continuously active". I know my players mix those two up all the time, so I wouldn't be surprised if others do, as well.

well from my experience these sort of problems crop up because of typo's.

Because doom is a non-area effect spell, but rather a medium targeted spell, I would say that it should be "at will", but a nice effect would be a 30ft radius will save dc (caster lvl required to make the item) or be doomed. Also you could add in additional effects such as negated by paladin's Aura of Courage or even have both effects suppress each other.