Daniel and Jude, thanks for your replies.
I'm sorry to say that I tried the suggested instructions below but got nothing, at least, nothing I could use. I note that I got a beep right after entering the "gnome-terminal" command: it didn't wait for the down-arrow. In fact, the down-arrow didn't cause a beep at that point, though it did after two uses of the alt-tab keys. At no point did I get orca talking.
Setting DISPLAY to :0 did not help, not even when I included the command in /etc/profile, so that it was set to this after boot-up. the command "echo $DISPLAY" gave me nothing before. Since you wrote that it also gave you nothing, but you apparently can use orca, maybe it doesn't matter. But if it doesn't matter, of course, why have I received error messages saying that it does?
Thanks again, though. Of course, I welcome any other suggestions for solving this problem. (I'm beginning to fear that this is some quirk of my system, like whatever prevented me from installing FC6 from CD's but didn't prevent installation from an image on the hard drive.)