[narfforc]

Then until Sauron either won or lost, the curse had no power, and when Sauron did lose, Isildur had the One Ring. Something gave power to the curse, whether it be Eru or the Ring, and that something had to be far more powerful than what was inherant in man, for it to withold the Gift of Iluvatar. The One Ring had already done this by ensnaring the Nazgul, it is not a great leap to think that Isildur could do something similar, but only with the aid of the Ring, Isildur was mighty amongst men, and the Numenoreans were great men. The Ring gave power according to the native power of the bearer, there was a great difference between Isildur wearing it and the halflings.