This is a question (or in some cases a blatant statement) I've seen many times. A statement which the ultimate answer to is no. To understand the true nature of these dark objects we must first look at their creators and their intentions:
Mairon (Quenya: The Admirable), later known as Sauron (Quenya: The Abhorred), was one of the immortal spirits known as the Maiar. Mairon was, at most, the most powerful Maia, and at least an extremely powerful one. Mairon was corrupted by the Valar known as Melkor (Quenya: He Who Arises In Might), later named Morgoth (Quenya: Dark Enemy) by Fëanor (High King of the Noldor). Mairon became Melkor's chief Lietuenant (equal only to Gothmog, Lord of Balrogs), which only added to Mairon's already impressive power. However, Melkor was eventually defeated by the Valar and cast into the Abyss. During the battle Mairon was wounded, which lessened the Maia's power. The strongest blow to Mairon's power, however, was the loss of Melkor. Without Melkor's power and influence (in addition to the wounds) Mairon's power grew to a fraction of it's former glory. This sudden weakening prompted a change in form (one of the traits of the Maiar). This new form was known as Sauron. Sauron then took refuge in the land of Mordor, preparing to avenge his master. It was at this point that Sauron crafted the Rings of Power (although the Elven rings were crafted by Celebrimor, an Elf). Soon after that, Sauron was taken prisoner (on purpose) by the Numenorians (very powerful humans). Sauron eventually influced the Numenorians into an attack on Valinor (the undying lands). This attack was thwarted by Eru (God, essentially) and Sauron lost much of his remaining power. Sauron forged the One Ring to make his power threefold that of Mairon's. The Ring DID in fact contain his remaining power and malevolence, although his soul had nothing to do with it. When the Ring was destroyed Sauron was not actually killed. Instead, all of his remaing power was so diminished that he could no longer gain spectral of copereal form. Sauron's spirt was sucked into the Void, where he now drifts aimlessly.
(NOTE: This is not Mairon's entire story. Nay, it is not even close. Even the events I mentioned are heavily snynopsized.
Tom Marvalo Riddle, more often called Voldemort (French- Vol De Mort: Flight From Death) or an array of hyphenated names, was born as the result of a Love Potion endused rape between an incredibly inbred squib (Merope Gaunt) and a muggle (Tom Riddle, senior). If only Merope hadn't married Riddle Sr... Then we could have added bastard to the list as well. Merope died giving birth to Tom Jr. and his father ran off as soon as the potions stopped. Unfortunately for the wizarding world, the Gaunts were the last descendants of Salazar Slytherin. This led to Tom being particularly gifted in area of Dark Magic. When Tom was only sixteen he split his soul for the first time, creating a Horcrux. However, Tom did not do this to become more powerful. Instead, he did it in an attempt to escape death. But there is one small point about the Horcruxes many do not relise. Most would think that his soul resides in equal parts within each object. They would be wrong. Every Tom made a Horcrux, it split the soul currently in his body. The percentages look like this:
Gaunt Family Ring: 25%
Slytherin's Locket: 12.5%
Hufflepuff's Cup: 6.2%
Ravenclaw's Diadem: 3.1%
Harry James Potter: 1.5%
Tom Marvalo Riddle: 0.7
This percentage scale easily explains why some of the Horcruxes had manipulative properties. It is now easy to see how the diary possesed Ginny while Nagini the Cup did not have much of an effect on the 'Golden Trio'. It also explains why the Locket created vivid hallucinations, hostile behaviour, and greed, but did not go so far as to possess the wearer. Perhaps this is also why Voldemort fell in the end. Perhaps he simply could not face the power of a good soul.
Let's do a final Ring vs. Horcux comparison:
Influnce by malevolence and malice
Forged by a Maia
Created as a conduit for the multiplication of power
Influnce by an evil soul attempting to assault the mind
Made by a mere human
Used to avoid death
As you can see, the One Ring is most certainly NOT a Horcrux. This should answer the fated question once and for all.