JOEL - Here are the scriptures you refered to:

23 The same day came to him the Sadducees, which say that there is no resurrection, and asked him,
24 Saying, Master, Moses said, If a man die, having no children, his brother shall marry his wife, and raise up seed unto his brother.
25 Now there were with us seven brethren: and the first, when he had married a wife, deceased, and, having no issue, left his wife unto his brother:
26 Likewise the second also, and the third, unto the seventh.
27 And last of all the woman died also.
28 Therefore in the resurrection whose wife shall she be of the seven? for they all had her.
29 Jesus answered and said unto them, Ye do err, not knowing the scriptures, nor the power of God.
30 For in the resurrection they neither marry, nor are given in marriage, but are as the angels of God in heaven.
31 But as touching the resurrection of the dead, have ye not read that which was spoken unto you by God, saying,
32 I am the God of Abraham, and the God of Isaac, and the God of Jacob? God is not the God of the dead, but of the living.

You are right when you say that the Saduccees did not believe in the resurrection. Because of this they were trying to trick Jesus into saying something contrary to this belief. He countered this by reminding them of what was already recorded in the scriptures about resurrection(Verses 31-32)
When Jesus said, "For in the resurrection they neither marry, nor are given in marriage,"(Verse 30) He is talking about those who are not sealed to each other in the New and Everlasting Covenant of marriage as performed in the temples. Those who are only married civilly will not remain together into the resurrection. They will only exist as ministering angels as spoken of in verse 30 and in D&C 132:16:
"Therefore, when they are out of the world they neither marry nor are given in marriage; but are appointed angels in heaven, which angels are ministering servants, to minister for those who are worthy of a far more, and an exceeding, and an eternal weight of glory."
In the scenario that the Saducees presented to Jesus they said "Now there were with us seven brethren:"(Verse 25) Since they were brethren of the Saducees, Jesus knew that they would not have been married under the covenat, and so this is why He told them that their marriage would not be valid in the next life.
When Jesus ordained His Apostles and gave them priesthood power He said:
"And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven."(Mat 16:19)
They would now have the power and authority to bind couples in the eternal marriage covenant on earth that would be bound in heaven as well.
And in talking about marriage Jesus said,
"Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder."(Mat. 19:6)
In other words, once God has joined two people together, through an authorized representative, no other earthly man can declare that they can ever be separated.
And in the Old Testament “whatsoever God doeth, it shall be for ever.” (Eccl. 3:14.)
Paul declared that “neither is the man without the woman, neither the woman without the man, in the Lord.” (1 Cor. 11:11.)
Not much else is said specifically about the eternal marriage covenant in the Bible. We must rely on later-day revelation(D&C 132) to understand the subject more completely.