2
flipse,
There's quite a few themes that do this using Smarty... I'd recommend you just 'grab' some of the code out of one of those as a starting poing. You can do things like:
<{if $xoops_isuser}> Welcome <{$xoops_uname}><{else}><a href='<{xoAppUrl user.php}>'>Logina><{/if}>
You can also use <{$xoops_isadmin}> to display info only for administrators, etc... There's a lot of other smarty variables you can use in the template to customize it. You can of course also make a custom block only visible to Admins, specific groups, etc. to display content for them only...