Windows XP on two computers.?
I think on the second computer when you try to activate windows you will be unable to do that, because hardware is changed. Then you will have to call support and they will see that computer hardware is diferent then as it was first time. So you should be fine using second windows for the 30 days, until dead line for activation.
Your previous install of windows XP will function fine. Microsoft would say you need to by another copy of XP. Until you do this both your laptops will run fine. When you get the other copy of XP you will not have to install it, it will only be used to verify you have pruchased two copies of the OS. If microsoft ever came to your home and asked to see all the computers you are running xp you would show them you have two regitration numbers.