Hi Denise,
I just bought a CD of Premiere Elements 9, too, 2 days ago. Before this, I downloaded that PE 9 tiral version for 30 days and played with a bit. I like it and found it much better than my current Pinnacle Studio v.10.
When I put the CD without uninstalling the trial version, the install wizard made me to uninstall it. So, I simply followed the guidance. Then, only after removing the trial version, it started to install. The procedure took about half and hour but went smoothly till the end. My computer is Windows XP sp3 and I have already Photoshop CS3 on it. So I bought PE 9 only.
I wonder if your problem is related to Photoshop Elements 9? What if you install first PE 9 and then photoshop afterwards, if the error persists?
Hope you