You can retrieve the username and password using the $xoopsUser object. I think that the password will be retrieved as md5 format(anybody know this for sure?).
To retrieve the username from the currently logged in user:
$username = $xoopsUser->getVar('uname');
To retrieve the password from the currently logged in user:
You must go to Admin Panel->System->Preferences->General Settings. From there, you can make it your default theme, or make it selectable in the list by going to Selectable themes and holding CTRL button down and clicking on the theme you would like available.
You might check out the Registration Keys module. It sounds like it might help you out some. I haven't used it, but I was surfing through the module repository and found it.
Go to the admin panel, System -> Blocks. Go all the way to the bottom, where you can create a new block. For the block type, you will need to specify Center Block-Center. Give it a title, and paste your code from Frontpage into the content area, and you should be set. Let me know if that is what you needed.