Okay I have an update! I think it's now solved.
For the help of others (and myself in the future if/when I have the same problems), I'll post things that I and reviewed to help figure this out but honestly, I don't know exactly what I did that worked.
Here's one of the threads I referenced:
I ended up at this page because I had come across this post that provided some information about creating a Facebook app and having content posted to your wall...
But I got an error with those instructions too. Error 100.
So I reviewed what was said on this thread here:
And saw there was a manual hack for the theme/index.php page
I tried that, and clicked the link to create the permissions, but I came up with the same page that told me what my Id was and that I'd need to enter it into WPBook's settings page on WordPress. There was the link to click to trigger extended permissions and then "Success" when that was clicked. However, I did that before and the only thing I was able to connect was to my personal FB page.
So I changed theme/index.php back to the way it was before... and I tried clicking on the link in the WPBook set up to get the permissions to work again...but THIS TIME it was different.
Now what I don't know was whether or not the old theme/index.php was the one it was relying on or the new one...but whatever...
The point is...this time in addition to giving me my ID, there was a NEW link on the page that dealt with granting STREAMING PERMISSIONS that was not there before.
So I clicked on it and lo and behold, I got the Facebook prompt to allow to post to the Fan Page Wall!
I went to my fan page to confirm that this worked. I clicked on Edit Page in my fan page, looked at my application... did NOT see "additional permissions"...but when I clicked on Application Settings, a new tab was there for additional permissions. And sure enough, the settings were in place to post to the wall.
I went back to the blog and posted an entry ...and it posted to the Wall. Success!
Only hitch now...and I'll see if others have had a problem with this or not...but previous posts did not move over and I did check that box and post the number of previous posts to go. Beyond that...we're good.