So, it seems that there may have actually been a bug in kopete 0.8.4 and earlier that is now fixed in 0.9.0...
First off, you can ignore warnings about not being able to validate ssl certificates. You'll get these errors connecting to any jabber server using a self-signed certificate. Since getting a certificate signed by a recognized signature authority costs money, and most jabber servers are set up by volunteers, you'll need to ignore these warnings with most servers. When the warning pops up, there's a check box that will cause kopete to ignore this error.
As for not being able to log in to our internal jabber server, in 0.8.4, I had "Allow plain-text password authentication" turned OFF. This worked in 0.8.4 and earlier versions of kopete. However, it does NOT work in 0.9.0. However, once I enabled plain text passwords in 0.9.0, I was able to log in. I can only figure that prior to 0.8.4, kopete was falling back to plain text even if you told it not to. Now that this is fixed in 0.9.0, my incorrect account settings stopped working.