to any computer in range which has a wireless adapter. In theory each computer's adapter will receive the router's signal and Windows will offer you the connection - all you have to do is tell it to connect.
The fact that only one machine can connect at any one time may be due to a variety of reasons - one of which may be an IP addressing issue. To be honest, your problem is such that finding a solution via this thread could be rather long-winded, and to begin with I would recommend that you start from scratch. Reset the router to its factory state, using the reset button that's on the case somewhere. Then use one of the laptops to set it up again, following the manufacturers' instructions to the letter.
Try tht, and come back to your thread with the results - if you still can't get a connection on both computers we'll take it from there.