user_relationships and facebook-style statuses integration: Block showing only my friend´s statuses

That's already a feature. Use the "Facebook Status UR Recent Updates" block. See documentation if you need help.

First refresh your cache. I think in 6.x that's under ?q=admin/settings/performance, but I'm not sure whether it clears the entire cache or not.

If that doesn't work try updating the weight of the facebook_status module in the system table in your database to -1. That probably won't fix anything, and in fact might break something, but if it works that's an easy fix.

There shouldn't be any conflict with other modules. Are you looking under ?q=admin/build/block or just expecting the block to show up on it's own?

Also, whenever you report a problem like this, you should state the type and version of PHP and SQL you're running. Otherwise it will usually be assumed you're on PHP 5.1 or later and MySQL 5.0 or later.

Anyway, the code for the block is pretty short, so if worst comes to worst you should be able to just stick this somewhere on your own.

  //You MUST set $ur_rtid to the RTID of the relationship type you want to use before executing this code.
  $content = facebook_status_get_rel_status($ur_rtid);
  $content = facebook_status_list_render($content);
  if ($content) {
    $content = '<div class="facebook_status_block_rel">'. $content .'</div>';
    echo $content;
  }

Anything that starts with a dollar sign ($) is a variable. That means it represents something, in this case a number. You have to store the number in the variable before you use it in the rest of the code; for example this code will pass '3' to the function:

$variable = 3;
this_is_a_function($variable);
//You can't assign a value to a variable while it's being passed as an argument, so this won't work:
this_is_another_function($variable = 3);
//Variables automatically have a value of FALSE if you haven't assigned them a value before.

You don't really need to do that though, since you already know what RTID you want to use. Just do it like this instead.

  //RTID = 1.
  $content = facebook_status_get_rel_status(1);
  $content = facebook_status_list_render($content);
  if ($content) {
    $content = '<div class="facebook_status_block_rel">'. $content .'</div>';
    echo $content;
  }