Installing Move Media Player on Safari Finishes with Errors

[Keldud7]

Hi there, fine mac people. I was having trouble downloading and installing a media player needed to view video on oprah's website. It would not work at all directly from the site, but once I downloaded from the link itself, it would download, but after installing it would say "Finished with Errors: Error 256." I found a thread in apple's forums that gave me a solution, however, I want to know why I couldn't/can't install it. The solution was to create a new user account and download it using that account and it worked. So I moved the file into the plug-ins folder and all is dandy. This led me to believe my user account is defective since the new one works so well.
But why won't my user account work to install it the media player? I repaired disk permissions. No problems there now. I even booted from Tiger's disk and repaired them there too.
What can I do? A little history about my computer: I was running Leopard on my powerbook G4 and kept getting frustrated with little incompatibilities that I went back to Tiger, a couple times. Is there a way to completely start over, and install Tiger again once and for all? Any other suggestions? Thanks so much.