Technical Question

I would be grateful to whoever can offer some help.
I am trying to uninstall my iTunes so I can download it all over again. But every time I do that it tells me that I don't have sufficient access to system administrator. I thought I was the system administrator. Also, if I try to run the old iTunes, it tells me I don't have Quick Time, when in fact I do. I tried to download another Quick Time without iTunes, that didn't work. This whole problem started when I downloaded last night the new iTunes version (I think 9.0), during installation, it told me I did not have the proper Quick Time. When I tried to go back to my old iTunes, it did not work. Now I can't uninstall Quick time or iTunes and I can't play my old iTunes. Weird.
Thanks for your attention and help on this matter.
I am trying to uninstall my iTunes so I can download it all over again. But every time I do that it tells me that I don't have sufficient access to system administrator. I thought I was the system administrator. Also, if I try to run the old iTunes, it tells me I don't have Quick Time, when in fact I do. I tried to download another Quick Time without iTunes, that didn't work. This whole problem started when I downloaded last night the new iTunes version (I think 9.0), during installation, it told me I did not have the proper Quick Time. When I tried to go back to my old iTunes, it did not work. Now I can't uninstall Quick time or iTunes and I can't play my old iTunes. Weird.
Thanks for your attention and help on this matter.