I just played with it and got the avatar to work. You will need to format it (image size, change message, etc.) yourself:
PHP Code:
$avatar = vB_Api::instanceInternal('user')->fetchAvatar(vB5_User::get('userid'));
$user['avatarpath'] = $avatar['avatarpath'];
if (!vB5_User::get('userid') OR vB5_User::get('userid')==0) {
echo '<img src="http://fansfoot.com/forum/images/misc/signup.png" alt="sign up" />';
} else {
echo '<img src="'. $user['avatarpath'] .'" />';;
}