Stop a running opponent.

[Vendarien]

I am trying to find a magical item or enchantment I can get for a weapon that will help me stop an opponent from running something that can be used at some sort of range. we are doing a low power game with no caster in the group and we had an opponent run away from the party problem is if he has greater speed than the rest of the party and we have no idea how to stop that kind of thing from happening.

[Grod_The_Giant]

Bolas? Nets?

[Diachronos]

Nets and bolas would work. You might also want to consider tanglefoot bags, or an Anchoring weapon if you're playing Pathfinder (not sure if there's something similar in 3.5).

If you have someone with Use Magic Device, maybe a scroll/wand of Grease?

[Vendarien]

Bolos is ok but preferably something a bit longer ranged. A net has a max range of 10 feat witch makes it pretty bad for trying to stop an already running opponent.

[VoxRationis]

Second the bolas. Magic isn't necessary. If you're trying to confine something larger, such that trip is unfeasible, use caltrops (though that takes more preparation or a jury-rigged delivery mechanism).

[Sith_Happens]

I've found that rendering someone dead or unconscious is usually a good way of impeding their movement.

[Biffoniacus_Furiou]

Earth Devotion feat in Complete Champion, you basically stomp your foot and the ground breaks up where you desire, creating difficult terrain. Note that running on difficult terrain requires a balance check, including if the ground you're running on suddenly becomes difficult terrain. Earth Devotion is an immediate action to activate, so you can use it in response to what someone else is doing when it's not even your turn. It's also perfect for automatically ruining an enemy's charge, since you're not allowed to charge over difficult terrain.

[jiriku]

Low-power campaign? Buy a horse. Ride him down next time.

[Runeclaw]

Low-power campaign? Buy a horse. Ride him down next time.

Or wardogs - good movement speed, good tripping capability. And a real-life law-enforcement technique!

[Kyberwulf]

Harpoons? :D