user information in header

[krike]

I would like to modify a template. in the left part of the header I would like to display the username of the member (sort of welcome message) and when not registered a link to registration page or login.

I would also like to know how can I display the total amount of logged in users and eventually the guests

what is the code for this?
site is -> http://iv-designs.org/vb/forums.php

thanks