iMac displaying black frames - I want them gone

Hello!
A few days ago my iMac (2GHz Intel Core Duo - OS 10.5.6) started displaying black frames around selected items on the desktop or text boxes on websites. Sometimes they linger in place briefly, after I've scrolled away from their original spot. How can I get rid of them?

Another thing I noticed that coincided with the appearance of the frames, was that my Apple menu displays 2 Restart commands, 2 Shutdown commands, and 2 Log Out commands. When I choose Shut Down, the computer goes into it's shutdown sequence, without prompting me for confirmation, which it always used to do. Any ideas what the cause of this might be, and how I can fix it?

Thanks for any help!

Here's a screen shot of the frame as I was about to submit this thread.

http://www.mac-forums.com/forums/os-x-operating-system/145648-black-boxes-around-places.html

http://www.mac-forums.com/forums/os-x-operating-system/105671-black-boxes-appearing-my-screen.html

http://www.mac-forums.com/forums/os...021-black-outline-around-clickable-areas.html

http://www.mac-forums.com/forums/os...oxes-appearing-around-dialogue-boxes-etc.html

http://www.mac-forums.com/forums/os-x-operating-system/85943-help-weird-black-boxes.html

http://www.mac-forums.com/forums/os-x-operating-system/46960-black-outline-boxes.html

http://www.mac-forums.com/forums/os...m-seeing-double-menu-options-weird-boxes.html

....and

Mac OS X 10.4: Computer speaks unexpectedly, or a black box unexpectedly appears around a file, folder, or other item

Thank you and forgive my lack of searching!