[Elrian]

It was Sauruman that hurled the snow at them from Isengard not mordor, and i agree with Marilpajgfbvkyklaobvuy (sp) the dead Marshes where a far more complicated magic than just a spell of Sauron, like the paths of the dead which i believe to be Gondolin. Perhaps the dead marshes wher a result of Morgoths and Saurons torment and torture over thousands of years that left many angry uneasy sad gory scary unimaginable uneasy spirits but not a direct spell, and even if Sauron could do such magic when Sam and Frodo where their Sauron did have enough power to take phisical form much less mantain a magic as terrible and gutrenching as the dead marshes.
but thats just my two lembas worth

In the movie it was Saruman, not the book.

I wonder if this is a contrivance of the Enemy,' said Boromir. They say in my land that he can govern the storms in the Mountains of Shadow that stand upon the borders of Mordor. He has strange powers and many allies.
His arm has grown long indeed,' said Gimli, 'if he can draw snow down from the North to trouble us here three hundred leagues away.'
His arm has grown long,' said Gandalf.

The Paths of the Dead were not Gondolin, which sank with the rest of Beleriand after the First Age.

That we shall know if we ever come to Erech,' said Aragorn. 'But the oath that they broke was to fight against Sauron, and they must fight therefore, if they are to fulfil it. For at Erech there stands yet a black stone that was brought it was said from Numenor by Isildur; and it was set upon a hill, and upon it the King of the Mountains swore allegiance to him in the beginning of the realm of Gondor. But when Sauron returned and grew in might again, Isildur summoned the Men of the Mountains to fulfil their oath, and they would not: for they had worshipped Sauron in the Dark Years.
Then Isildur said to their king: "thou shalt be the last king. And if the West prove mightier than thy Black Master, this curse I lay upon thee and thy folk: to rest never until your oath is fulfilled. For this war will last through years uncounted, and you shall be summoned once again ere the end." And they fled before the wrath of Isildur, and did not dare to go forth to war on Sauron's part; and they hid themselves in secret places in the mountains and had no dealings with other men, but slowly dwindled in the barren hills. And the terror of the Sleepless Dead lies about the Hill of Erech and all places where the people lingered. But that is the way I must go, since there are none living to help me.

The Dead Marshes were not something contrived by Morgoth, The Dead Gollum speaks of in this passage are from the Battle of Dagorlad during the last Alliance, Morgoth was long gone by then. The graves of the fallen were eventually swallowed up by the Marshes.

Yes, yes, said Gollum. 'All dead, all rotten. Elves and Men and Orcs. The Dead Marshes. There was a great battle long ago, yes, so they told him when Smeagol was young, when I was young before the precious came. It was a great battle. Tall Men with long swords, and terrible Elves, and Orcses shrieking. They fought on the plain for days and months at the Black Gates. But the marshes have grown since then, swallowed up the graves; always creeping, always creeping.
But that is an age and more ago, said Sam. The Dead can't really be there! Is it some devilry hatched in the Dark Land?
Who knows? Smeagol doesn't know, answered Gollum. You cannot reach them, you cannot touch them. We tried once yes, precious. I tried once; but you cannot reach them. Only shapes to see, perhaps not to touch. No precious! All dead.