Taxonomy and CCK are two techniques that are used often in Dr installations. A lot of modules are building upon them.
But is it possible to combine them? I searched a lot but i can't find the answer. When creating a node, and term 1 is selected, only the CCK fields belonging to term 1 should be shown (or accesible). When term 2 is shown, the corresponding CCK fields are used.
In this way, you can create something like this in the add/node form:
title: a new car
content: blabla
term: cars
=> CCK fields "engine power" and "tyres" shows up / are usable.
======
title: a tree
content: blabla
term: plants
=> CCK fields "kind of plant" and "foobar" shows up / are usable.
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I hope somehow this is possible to get to work.

Comments
Lenses ?
There was a discussion about something similar - someone had written some code, don't know if it ever came out as a module. Check this thread http://groups.drupal.org/node/8361