It will run on XP, but you must activate it first just like the real deal. Then the clock starts ticking for your 60 days trial. Don't convert any of your 2003 files and don't save anything in the 2007 format unless you intend to install Office 2007. Just play around with it during the trial. To activate, open Word or any one of the applications in Office, go to Help, Activate.

I downloaded a trial version of Office Standard 2007 a couple of weeks ago.  Installed all the programs and they all appear to be 100% functional.  I was very skeptical about the 07 version at first, but after using it for these two weeks I must say that I really like it.  Takes awhile to get used to, but after a bit you will adjust.  The one thing I wish I could change is to have more than three skin options. (Blue, Silver, Black).