I have iTunes in OS X set up just the way I want it. To get iTunes in 9 to use the same settings, in the Documents folder at the root of your drive, there is a folder called "iTunes." That hold your OS 9 iTunes data. If there isn't any music in there, you can trash it. Now, make an alias (it can be a regular alias... don't worry about a symbolic link) of the folder at ~/Documents/iTunes and put it in there, making sure it's still called iTunes. It's your iTunes data from OS X.
Then, your Library will be consistent from OS 9 to OS X. If you delete from one, the change will affect the other, since it's the same data.