How to get CCK optionsfield value, if I have the key for that value?
Node_load will return fully-populated node object. 

Value of cck fields in node object are usualy accessed in this way: 

 $my_node_object = node_load($nid);
 $myVar = $my_node_object-&gt;field_your_field_name['0']['value']


You can see what $node object contain if you do 

dsm($my_node_object); // Devel module must be turned on


Hope this helps.