I'm not sure if you are referring to a simple (ala Flickr) tag cloud, or something a little more complicated like Wordle.
Anyway, if you are looking for a simple tag cloud, it wouldn't be too difficult to implement it yourself (as long as you already have the ability to render HTML) as it is just changing the size and/or colour of each item based on its frequency (or some other measure).
If you want to use an existing library you could look at one of the opensource php versions, like Tag Cloud, put just run them locally on your machine using php rather than through a web server. Just install php and run php filename.php similar to how you would execute a python script.
Looking at the Wordle service, there appears to be no way to automatically create one, as they use a java applet to generate the graphics, which cannot easily be scripted using curl. They do have a question in their FAQ about an API however:
Could you expose Wordle as a web
service that generates images?
A scalable web service should take no
more than a few tens of milliseconds
to do its work. To create a Wordle
requires multiple seconds in a Java
runtime. (That pretty animation is not
for show; it's really laying things
out during the animation). Therefore,
Wordle will always apportion the
CPU-intensive stuff to you, the user,
and your CPU.
As of this writing, Wordle is
sustaining 10 hits per second. There's
no way on Earth to render Wordles at
that speed. Well there is a way, but
it involves way more money than I've
got.
Also, this previous question may help.