Yes you can do it. You must uninstall the trial first.

"newtonet" <newtonet@discussions.microsoft.com> wrote in message
news:E5F373E1-F43C-497A-99D1-E972CA81B9C1@microsoft.com...
>I have a laptop with Vista pre-installed. It came with a trial copy
>of
> Office 2007. The trial is over and I want to put the copy of Office
> Pro 2003
> on the laptop that I already own? Can I do this? If so, do I need
> to
> uninstall Office 2007 first?