Hi,
I've had the same problem with Blackboard (Safari 3.1.1 on MacOSX 10.4.11). The thing with Blackboard is that it uses javascript to fill the login form (and Autofill won't work).
My answer to that was to use
Safaristand, and to activate the Site alteration feature:
Go to your blackboard login page, don't fill anything.
Then go to Stand menu --> Safaristand settings --> Site Alteration
Make sure you have your blackboard page listed, check "Enable Site alteration", and check the second "Alter" line (the one which says "Javascript enabled" on its right). Uncheck "javascript enabled".
This will basically deactivate javascript on the blackboard login page.
Now put your credentials (login and password) on the blackboard page. Click "yes" when you're asked if you want to remember your password.
You'll get an error, saying you didn't provide any credential, but that's ok.
Now you can deactivate the site alteration altogether and close the page.
Next time when you go to the blackboard login page, just type the first letter of your username, and you'll see that Autofill has been activated! (and you can check that in Safari preferences --> Autofill --> User names and passwords --> Edit
Hope this helps,
ludo