Unable to delete files on desktop

My older brother lives in a nursing home where he uses his MacBook running (I think) Leopard. He is not too computer savvy and I continually have to "fix" things on his computer that he has messed up, which I'm happy to do.

He has two files on his desktop -- an empty folder and a .jpg downloaded off the Internet -- that I can't delete. When I try to move them to the Trash I am asked for his system password which I enter, to no avail. In "Get Info" the files don't appear to be locked or anything, and Read/Write permissions are checked for both. I have tried everything I know to delete these files but can't. They're not hurting anything -- but I'd just like to be able to delete them in an effort to keep his desktop organized.

Is there some way to "force delete" these files. Thanks for any help.