Your files should be safe. 2007 is only an upgrade to an existing version. So unless you created files using a feature available only in 2007 you should be safe. I use Outlook 2003 at work and don't have authorization to upgrade my computer so I am not 100% certain, but I would bet that if you played around on 2003 you should find your files.
I installed an older of MS office on my laptop (2003). It previously had a 2007 MS Office Trial. When the trial was over I installed the 2003 version, then (this is where the mistake was made) I uninstalled the trial. What this did was remove Outlook 2007, where I had very important files. I thought these were backed up with my mail host, but I don't think so. Are these files completely removed from my computer?

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