I would contact the company where you got the laptop from for an XP installation disc. They should have given you one when you got your PC>
As for two computers. There are lots of threads in teh helproom forum about this subject.
I believe you can use One original copy of XP on one desktop pc and one laptop pc.
If two of the same you should really have two versions of XP.
Silly really as they are both your pcs.
I wuold go to microsoft.com, i am sure they have some information about licenses.