KB, I'm not running 10.5 (I'm at 10.4.11), but I am running iTunes 7.6.something which allows you to have more than one library and I would think that's similar to what you are hoping to do.
When you launch iTunes, hold down the OPTION key. A dialog box will come up and ask you about choosing a library. Your default should still remain your default (mine has at least), but now you can navigate to any iTunes library -- including one on another drive.
Let us know how things work out.