I currently have an unlicense version window xp professional on my
Sony laptop.(Don't even ask...)
My laptop came with it's own window xp home (Certificate of
Authenticity sticker at the back of laptop said so).  But i dont' have
any of the CDs.
My question is that how do i reinstall the xp home without any CDs? 
Does this means that i have to buy the operating system again?  Do i
contact Sony? or Microsoft?
If i purchase a copy of windows xp professional, is there a way to fix
my unlicense problem without a partition?

There should be a law stating that if a manufacture sells you hardware
with software preloaded, they must send you the installation disks
with the hardware IN THE SAME BOX.

That said, call Sony and tell them to send you YOUR XP Home install
disks. You might need to provide them with the serial number on the
authentication sticker.

If you purchase XP Professional you can update your current key with
your new legal one by going here:
http://www.petri.co.il/change_the_serial_in_windows_xp.htm

You should not have any problems at all if you purchase windows xp
professional and install it (just put in the cd and follow
directions). You want to get windows xp professional with service pack
2 included for optimum security. I would even recommend installing and
using netscape navigator to prevent spyware (internet explorer which
is microsofts included internet browser is a large target for spyware
and viruses). I can also explain how to fix your unlicense problem and
keep your current partition if you email me or chat via aim or
messenger since it would take a while to explain here.

If you still want to install xp home ed
The best thing to do is to find a friend who has a disk copy of xp
(home ed) (this can be a challenge due to computer shops saving a
couple of dollars by not giving anyone a disk).
Another way you can get an xp disk is to use a P2P file sharing
program (e.g. Ares) and download it off someone elses pc - (you have a
licence for it after all) - Then you need to burn that copy onto a
disk.
#####  You need to be careful though as you will probably have to do a
full reinstall - You could lose some or all of the old files on your
computer - so if you can, back-up all the files and programs that are
precious to you  ######.  At least that way if you have to re format
your hard drive it isn't a problem.
When you have a disk, shove it in to your cd drive and follow the
prompts.  Enter your old licence number as stated on the shiny sticker
under your computer - and if you make it to this stage all should be
good.  Apparently the licence is not for a specific disc - but it is
for the generic program.
Good luck and try to befriend a computer geek.
j.