Is purchasing and using a laptop considered unlawful (haram) due to lying to one's husband by saying, "My friends bought it," when the truth is that her friends did not buy it?

You must repent to Allah for the lie of claiming that your friends bought computers.

As for the permissibility of taking the computer and owning it, it depends on the husband's knowledge of the reality. If he knew that he only gifted it due to the claim of your friends buying computers, and that if he had known the truth, he would not have gifted it to you, then it is not permissible for you to take it. You must return it to him or explain the situation and seek his forgiveness, because if someone is given something based on a description that the giver believed to be true, but the reality is otherwise, it is forbidden for the recipient to take it, and he does not own what he has taken.