It looks like aspell is installed. I got this back and a lot more.
"[root@small tmp]# aspell
Aspell 0.50.5 alpha. Copyright 2000 by Kevin Atkinson."
I did install the Ajax Spell Checker from the link you gave. But it looks like it's not working ether. It downloaded as a zip file. I unziped it right to "wordpress\wp-content\plugins" then deleted the zip file. It has a folder now in the plugins named "spell_checker" that's were all it's files are and one other, the "ajax-spell-checker.php" in in the plugins folder too. Is this the right way?
All I get when I click on the blue color text "Check Spelling" is "Error on page." in the buttum left corner. Nothing else happends.
If I click on the "Activat Spell Check while Typing" It makes a blank spot just over the part were you type and if I typed I only see the letters for a sec. and they don't move over to the right.
I can type in the blank spot but every thing I type is under line in read. Wrong or right words.
So it seems like this Ajax spell checker is harder to get working then the other one.