I ran into a problem after I enabled permissions on an external FireWire drive: my non-administrative user could not move anything on that drive to the Trash. When trying to "Move to Trash" any file or folder, the user was presented with the warning that "The item '[filename]' will be deleted immediately. Are you sure you want to continue?" The user could still use the Trash for items on the boot drive or in their home directory.
Despite numerous attempts at fixing the ownership and permissions of the files, the .Trashes folder, and the drive itself, I came upon this solution: delete the .Trashes folders, then relaunch the Finder. This recent hint discusses how to solve similar issues in one's home directory.
If you start in the Terminal as a non-administrative user, first switch to an admin user with:
su admin_username
Then move to the root of the affected drive and remove the .Trashes folder:
$ cd /Volumes/<volume name>
$ rm -rf .Trashes
Finally, relaunch the Finder by holding down the Control and Option keys while clicking on the Finder's icon in the Dock. The .Trashes folder will be recreated, and all users should now be able to use the Trash as expected.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060329130416101