Actually, now that I come to do it (delete and replace the WP-Admin and WP-Include files) I realize that I did that already as part of the upgrade to 2.0.1. My backed up files are from 1.5, and I’m not so sure it would be a good ideas to mix the two.
The only thing I can think of is that I was using WP-admin-tiger plugin, which makes for a cleaner admin interface than what 1.5 provides. I couldn’t deactivate it because I couldn’t access any of the admin pages, so I deleted it off the server. That’s the only thing I’ve done outside of the upgrade.