Do all Christians confirm that God (ie. one who creates the heavens and earth) and Jesus Christ are one? If God and Jesus Christ are the same why when Jesus Christ was on earth did he preach sometimes opposite to the old rules and regulations in the Old Testament?
It is my opinion that, by definition, all Christians believe that Jesus and God the father are one. That is exactly what Jesus said in John 10:30. Here, Jesus said to the people, "I and the Father are one." When Jesus said this, the people tried to stone him for claiming to be God. Jesus did not deny this charge.
Now, there are some supposedly Christian groups which deny that Jesus is God. For example the Jehovah’s Witness group says that Jesus is not God. The Mormon (LDS) group is confused on this as well. 1 John 2:21-23 states that anyone who is not clear on who Jesus is is a "liar" and an antichrist.
So, not all who claim to be Christians confirm that God and Jesus Christ are one, but I believe that, by biblical definition, all true Christians support this claim.
About Jesus preaching against the Old Testament, this is a false accusation. Jesus observed all the Law of Moses while alive. He was accused of breaking the commandments, but in fact, if he broke any "commandments" it was the traditions which the Pharisees and Scribes added to the Law. Jesus made a very strong positive statement about the Law of Moses in Matthew 5:17-20. "Do not think that I have come to abolish the Law or the Prophets; [a reverence to the Old Testament] I have not come to abolish them but to fulfill them. I tell you the truth, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished. Anyone who breaks one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven, but whoever practices and teaches these comands will be called great in the kingdom of heaven. For I tell you that unless your righteousness surpasses that of the Pharisees and the teachers of the law, you will certainly not enter the kingdom of heaven."
If you continue in Matthew 5, you will find that Jesus consistently supports the spirit of the Old Testament law and calls his people to an even higher standard of righteousness. It is true that after Jesus died on the cross, Christians are no longer required to obey the Law of Moses, with its animal sacrifices and so forth, but according to Jesus this is because he fulfilled the requirements of the Law of Moses and he has offered a better means of coming to God through his blood. This is a deep topic which needs a lot of discussion. My suggestion is that you consider reading the book of Hebrews to understand the relationship between the Law of Moses and the Law of Christ.