This is a truly weird bug.
I used the OS X system migration tool to configure my MacBook. The donor system was my old G3 iBook, with an old version of Classic. That version of Classic contained a file called "Finder Extensions Enabler".
OS X can't delete that file, nor can it delete an accompanying text file.
Why not? I don't know, but the Version string has an oddity. It contains the string [Nevin ":-)" Liber]. I'm betting the embedded quotes in the Version string has messed up OS X.
Update: I tried Onyx, but it couldn't get rid of these suckers. OS X Hints suggested Secure Delete, but that hung. Then I tried OS X Help -- it had quite a few tips. I noticed the file owners were another account, so, while they were in the trash, I changed ownership. Delete didn't work, but now Secure Delete did the trick. (Finder, File menu)
Update 2/5/07: Read the comments. The author of the version string responds! The limitations of ASCII are embedded everywhere, but Asian character sets will, one day, clean things up. This bug struck me again when I migrated from an iBook (that can run Classic) to my new MacBook. Secure Delete saved me again.