Here are some PHP snippets to display data from custom profile fields you can set up using the core profile module in Drupal 6. In this first example I have a custom user profile field that holds the user's location with the machine readable name of profile_location. The first block of code stores the location of the user who is logged in in the variable theLocation. The second block of code displays this value.

<?php
global $user;
profile_load_profile($user);
$user_location = $user->{profile_location};
?>
<?php print $user_location; ?>

Here is the PHP code that I use to display this code in a block on only the user's profile page. Put this code in the "Page specific visibility settings" with the "Show if PHP code returns true" option checked.

<?php
global $user;
if ($user->uid == arg(1) && arg(0) == 'user' && arg(2) != 'edit') {
    return TRUE;
}
?>