The information is all right in front of you on your site. Install Firebug and the Developer Toolbar for Firefox and you can figure out all the css and html.
You are on the right track so far.
Go to your Xen forum, view the source. Extract the html and css that are the relevant bits to the login box.
Paste said bits into your WP header template.
Dubug any code conflicts.
I suspect it will be some css files, a .js file which you may or may not need depending on if you are using it...
From what I gather that theme just styles WP to look like the Xen theme. Correct me if I am wrong. Not helpful in my case, but clever nevertheless.
I'm an idiot. I just noticed:
Admin CP -> Appearance -> Templates ->
In Lion the scrollbar is hidden until you scroll. I never hovered over...
Over the years I have used a lot of forums as well as lean heavily on Joomla and Wordpress for a main CMS. I don't usually bridge the user tables as it isn't normally necessary, but I do make sure all the scripts have the same looks.
In the past, when I wished to style vBulletin exactly how my...