[nsanden]

I do pretty much the same thing on my site. The way I did it was first check to see if the visitor has $_COOKIE['bbuserid'] set. If that is set, it means he is logged in, in which case you don't want to show the login form.

if($_COOKIE['bbuserid']) {
    //show login form
} else {
    //show user info
}

For the login form i made my own but made sure to include the required hidden input fields VB uses and post the script to VB's login.php page.

For the user information i ran a query against the vb_user table based on the $_COOKIE['bbuserid'] id.

Hope that helps.