should we have a hard copy of winXP while we are buying a computer

[Qiuli Han]

Hi everyone
i ordered my new dell computer last week and found it in front of my
door yesterday
but after i searched everywhere in the box i didn't see a hard copy (a
disk) of WinXP in there
well...it has the serial number on the computer case, does this mean i
can do re-installation of  WinXP by using any disk i find with this
key?
OR
should i have a hard copy of the pre-installed OS (could be any other
OS beside Windows) i purchased alone with my computer ( of course i
know i paid the OS while i am reviewing the order list)?

Q