Not sure if PrE8 Themes are 100% compatible with PrE 9, but if they are, then one should be able to Copy over the necessary files/folders to PrE 9. Unfortunately, I am not sure what exactly constitutes the Themes, and exactly what would be required. Others can point you to the folders and files necessary. I would definitely do a System Restore Point, prior to Copying over the necessary files/folders, just in case there is major incompatibility, and also take good notes on exactly what was Copied over and where.
Versions can change pretty drastically on how they function with add-ons, and features. Sometimes, it's just that Adobe has omitted some, but other times, things have changed too much to allow for that to work. Sort of like Brushes and Actions in Photoshop. For a few versions, the Copy over will work fine, but then with some newer versions, things have changed too much, and the older Brushes and Actions will not work in the newer version. It differs by version and also by what one is wanting to Copy - "sometimes the magic works, and sometimes it does not... " [Chief Dan George]
Good luck, and let us know if "the magic works."
Chuck, you should be able to copy the MOVIE THEMES folder (or any of its sub-folders) from C:\PROGRAM FILES\ADOBE\PREMIERE ELEMENTS 8.0\ to C:\PROGRAM FILES\ADOBE\PREMIERE ELMENTS 9.0\ and then, when you restart the version 9, version 8's themes should be in there.
Great to know. That was my thinking, and my hope, but I was just not sure if the Themes had been changed between PrE 8 & 9.
Good luck to the OP,