If the purchased copy is the same version as the pirate version (e.g.
XP Pro) then you can simply replace the pirated product key with the
legitimate one by using Windows XP Product Key finder from
http://www.webtree.ca/windowsxp/keyfinder.exe which includes an option
to change the existing product key to a valid one without doing a
reinstall.
Note that if the legitimate Windows XP version is XP Pro with Service
Pack 1 incorporated and the pirated version is just XP Pro (no Service
Pack 1) then this may not work.
In that case you may have to do a repair install as per the
instructions at
http://michaelstevenstech.com/XPrepairinstall.htm
And if the pirated version is XP Pro and the legitimate version is XP
Home then you will have to reformat the hard drive and install XP
clean on the empty hard drive then install the applications and
finally restore the data files from backups. Using the Files And
Settings Transfer Wizard (see
http://www.aumha.org/win5/a/fast.htm
by MVP Gary Woodruff) can greatly expedite this process should it be
necessary.
Good luck
Ron Martell Duncan B.C. Canada
--
Microsoft MVP
On-Line Help Computer Service
http://onlinehelp.bc.ca
"The reason computer chips are so small is computers don't eat much."