contextual and downward filterable tagcloud
What I think you are saying you want to do is this:


Grab all content that is tagged with a certain term, then
List in a block all taxonomy terms from that content


And if so, it's pretty straightforward to loop through a list of node and aggregate and each taxonomy term that is attached to each node, and then stylize a block of those terms, eg,

$nids= // execution results of a view or other sql that filters on a term;

$found=array();
foreach ($nids as $nid) {
   $node=node_load($nid);
   foreach ($node-&gt;taxonomy as $t) {
      found[$t-&gt;tid]=$t-&gt;name;
   }
}


which will (if my off the top of the cuff php code is accurate ;-) produce an array $found that is a list of terms that can be styled however you wanted in a variable or block, most simply like:

 foreach ($found as $tid =&gt; $name) {
    $content.=l($name,'taxonomy/term/' . $tid) . ' ';
 }
 return $content;


You can probably do all of this in a View itself with some funky templating, too, if you didn't want to create a module and/or theme preprocess function.