A follow up. I have the science and space/cosmos sections working now. I discovered that I had changed my password at the New York Times site itself, but hadn't updated the source link and the cookies in iSiloX!
But I still cannot get the education section working.
It's this page: http://www.nytimes.com/services/xml/.../Education.xml
Another odd thing I noticed is that the cookie NYT-S showed a different value for the science and space/cosmos sections! And they're different from what shows in Firefox, too! I'm pretty sure I simply copy and pasted the cookie into both cookie fields for the two sections--but they changed!
Well, solved that one, too! I copied and pasted from the science source into the education source and changed the final part of the url from "science" to "education"--that did it. There must have been a stray character or something in there (even though I compared them in a text editor and thought they were the same).
In any event, maybe my travails will help someone else (when all else fails, copy and paste the URL source link and change a few characters!)