I don't know how long the user names / passwords can be.
The style is only rudimentary, to show how this could look like the current design. It'll have to be tweaked later.
Valid, semantic, and accessible XHTML 1.1, once again :)
Some CSS "tricks" used (my apologies if you already know / use this, but I haven't seen them on GNU Herds):
Resetting margin and padding for everything at the start to prevent browser differences.
Floating the content div makes the border stick to the outline of the children.
text-align:
center; works for the children, while margin: 0 auto 0 auto; works for
the current element. The latter is useful when there is no children,
such as for <input>.
Instead of using <br>s,
you can set display: block;. The element will then take the full width
of the containing element, pushing any other content down.