Greetings maroon1,
1-Would all Non-Muslims go to hell for eternity according to Islam ?
Whoever denies Allah, or worships something else besides Him, or takes other gods instead of Him, or says that He has a wife or son, or that the angels are His daughters, or follows a law other than that which He revealed to judge between people in truth, or turns away from His religion, will be doomed in the Hereafter to the eternal punishment of Hell.
However, it is part of the justice of Allah that He does not punish any people until He has first sent a warning to them and unless there is evidence against them. Allah does not treat anybody unfairly. A person who has never heard of Islam or the Prophet (peace and blessings of Allah be upon him), and who has never heard the message in its correct and true form, will not be punished by Allah if he dies in a state of kufr (disbelief). If it were asked what his fate will be, the answer will be that Allah will test him on the Day of Resurrection: if he obeys, he will enter Paradise and if he disobeys he will enter Hell. The evidence for this is the hadeeth of al-Aswad ibn Saree’, who reported that the Prophet of Allaah (peace and blessings of Allaah be upon him) said:
“There are four (who will protest) to Allah on the Day of Resurrection: the deaf man who never heard anything, the insane man, the very old man, and the man who died during the fatrah (the interval between the time of ‘Eesaa (Jesus, upon whom be peace) and the time of Muhammad (peace and blessings of Allaah be upon him)). The deaf man will say, ‘O Lord, Islam came but I never heard anything.’ The insane man will say, ‘O Lord, Islam came but the children ran after me and threw stones at me.’ The very old man will say, ‘O Lord, Islam came but I did not understand anything.’ The man who died during the fatrah will say, ‘O Lord, no Messenger from You came to me.’ He will accept their promises of obedience, then word will be sent to them to enter the Fire. By the One in Whose hand is the soul of Muhammad, if they enter it, it will be cool and safe for them.”
According to another report, he said: “Whoever enters it, it will be cool and safe for him, and whoever does not enter it will be dragged to it.”
(The hadeeth was reported by Imaam Ahmad and Ibn Hibbaan, and deemed saheeh by al-Albaani, Saheeh al-Jaami’, 881).
So everyone who hears the message of Islam in a sound and correct form (and rejects it), will have evidence aginst him. Whoever dies without having heard the message, or having heard it in a distorted form, then his case is in the hands of Allah. Allah knows best about His creation, and He will never treat anyone unfairly. And Allah is All-Seer of His slaves.
There is another thread about this topic which contains other useful links, which can be found here:
http://www.islamicboard.com/discover-islam/30127-who-will-enter-hell.html
2- If a Muslim don't pray, and don't practice his religion at all, but he believes in God and that Mohamed is messenger of God, would that Muslim go to hell for eternity or he will go to hell temporary and then to heaven ?
With regards to sinners such as the one who kills a person unlawfully, the one who commits adultery, the one who disobeys his parents, the one who consumes interest, the one who drinks alcohol and so on; if they die in their sin and they are Muslims, then they are subject to the will of Allah, as He says (interpretation of the meaning):
“but He forgives except that (anything else) to whom He wills…”
[al-Nisa’ 4:48]
So if Allah wills, He will forgive them because of the righteous deeds with which they died, such as their believing in Allah alone (Tawheed), their sincerity towards Allah and their being Muslims, or because of the intercession of those who intercede for them, as well as their Tawheed and sincerity.
Or Allah may punish them with a temporary abiding in Hell, in a manner commensurate with their sin, and then He will bring them forth therefrom.
With specific regards to those who don't pray, then there is a difference of opinion on this matter. Prayer
is the greatest pillar of Islam after the testimony of faith, and whoever does not pray will have his good deeds rejected. The Prophet (peace and blessings of Allah be upon him) said, "What is between a person and committing shirk (associating partners with Allaah) and kufr (disbelief) is abandoning the prayer." (Narrated by al-Tirmidhi, 2766. Classed as saheeh by Ibn Maajah, 1078, and by al-Albaani).
Therefore some scholars hold that a person who abandons his prayer is out of the fold of Islam, and what was mentioned earlier regarding only temporary punishment in Hell may not apply in this case. The other scholarly opinion is that the person who neglects prayer is still a Muslim but has very weak faith.
I hope this has helped to answer your questions, and Allaah, Exalted be He, knows best.
Peace.
For the hadeeth that thirdwatch posted (I deleted his/her reply), there is a thread that refers to it, 
