If domain based, sounds like a GPO was applied incorrectly.
Also, I have seen a few software packages in the past actually require you to be logged in under the Administrator account, not just be in the Admin group. I know it's goofy, but it happens
I bought the PC and XP Pro separate. Installed the XP Pro and a few other items. Now trying to install Cyberlink PowerDVD Ultra from an original CD from a Retail Box. PC is stand alone.
So I take it other programs install fine? Seems odd and since you did a clean install on a stand alone system. For now I would suggest checking the local security settings.
I am on my phone for this post, so I can look it up right now.