While using Virtual PC is an option the OP subject heading says 'older
version of xp over new version' It should be remembered that, for licencing
purposes, a Virtual machine is actually classed as 'another' pc even though
it is on the same pc. Therefore if, for example, you already are running XP
on your PC and you then install the 'same' copy of XP onto a Virtual machine
you would 'technically' be in breach of the End User Licence agreement. The
same applies to installing the same copy of XP on another partition on the
same machine.
Of course if you are using Virtual machine to install 'older' copies of an
operating system, i.e, Win 98, ME, 2000 etc on the same machine as the one
containign XP, then, so long as you have a valid licence for this older
software then you should have no problem.
--
John Barnett MVP
Associate Expert
http://xphelpandsupport.mvps.org
http://vistasupport.mvps.org
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