How do Calvinists explain God's wanting no one to perish and electing some to judgement? I have two ideas that have support in the bible, but seem to contradict! Please help! I am looking for a Calvinist/Evangelical answer.

These two verses have the general effect that God does not want anybody to go to hell. 


  The Lord is not slow in keeping his promise, as some understand slowness. Instead he is patient with you, not wanting anyone to perish, but everyone to come to repentance. (2 Peter 3:9, NIV)


and


  who desires all people to be saved and to come to the knowledge of the truth. (1 Timothy 2:4)


However, God clearly claims his sovereignty over souls going to heaven and hell. He decides who goes to heaven, and who doesn't.


  And the LORD said, "I will cause all my goodness to pass in front of you, and I will proclaim my name, the LORD, in your presence. I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion. (Exodus 33:19)


and 


  21 Does not the potter have the right to make from the same lump of clay one vessel for special occasions and another for common use? 22 What if God, intending to show His wrath and make His power known, bore with great patience the vessels of His wrath, prepared for destruction? (Romans 9:21–22)


So one 'will' of Seems to be, he doesn't want anyone to go to hell. On the other hand, he clearly says he sends people to hell according to... a different will?! 

I think the same problem applies in 'God doesn't want anyone to commit murder in general, however he clearly wanted the Jews crucify the Son of God' 

Can anybody explain to me how Calvinists resolve these tensions?
The typical Calvinist response to this question is captured well by Wayne Grudem in his Systematic Theology:

[1 Timothy 2:4 and 2 Peter 3:9] speak of God's revealed will (telling us what we should do), not his hidden will (his eternal plans for what will happen).  The verses simply tell us that God invites and commands every person to repent and come to Christ for salvation, but they do not tell us anything about God's secret decrees regarding who will be saved. (32.D.6)

It's true that some Calvinists take a different approach and suggest that &quot;all&quot; in 2 Peter 3:9 refers only to the elect, and the &quot;all&quot; in 1 Timothy 2:4 could be interpreted as &quot;all sorts of people.&quot;  John Piper explains this in more detail in his article, &quot;Are There Two Wills in God?,&quot; but like Grudem he too argues for &quot;two ways of willing&quot; in God.  Piper draws on one of the classic proof texts for this idea, Acts 2:23:

this Jesus, delivered up according to the definite plan and foreknowledge of God, you crucified and killed by the hands of lawless men. (ESV)

That is, the most heinous crime in all of history, the brutal murder of the Son of God, was part of God's &quot;plan&quot; (his &quot;secret&quot; or &quot;decretive&quot; will).  And despite that, it's clear that the men who killed him sinned – they violated the commandments of God (his &quot;revealed&quot; or &quot;preceptive&quot; will).
Let's look at a few more verses that are used to establish this idea.  First, here are some that describe God's will as fully independent and never failing:

Psalm 115:3: Our God is in the heavens; he does all that he pleases. [ESV]
Daniel 4:32: the Most High rules the kingdom of men and gives it to whom he will.
Romans 9:18: So then he has mercy on whomever he wills, and he hardens whomever he wills.

These verses above describe his &quot;decretive&quot; will.  But the following verses show that his &quot;preceptive will&quot; is regularly disobeyed:

Matthew 7:21: &quot;Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven.&quot; [cf. Matthew 12:50]
Ephesians 5:17: Therefore do not be foolish, but understand what the will of the Lord is.

For more analysis of this and my answer to a similar question, see How can God be Sovereign (in the Reformed sense) if a man can ignore His call to repentance?  Piper's article also gives a thorough defense of this type of distinction.
One closing thought: it's worth noting that Calvinists argue that this difficulty also applies to Arminianism.  Arminians must also reconcile &quot;God desires that every individual be saved&quot; and their belief that not every individual is saved (at least those who reject universalism and affirm God's omnipotence).  Their explanation, Grudem says, is that God desires humans to have free will more than he wants them to be saved, and that this is a manifestation of the two aspects of his will.  How Arminians would say they deal with this issue is a subject for another question.