Hi

I was very interested in your tutorial on Custom Post Types and Fields

However from the user side, what they see is a sort of drop down directory or search facility. I was wondering whether it was possible to adapt this to custom tag clouds.

Basically I have a couple of people interested in doing guest blogs but I want to keep their blog posts in a separate subject tag cloud - (tag cloud for community enterprise and another tag cloud for sustainable energy). Ideally these two tag clouds would be kept separate from a normal, generic tag cloud of posts that I do.

Is this possible?

You should be able to generate custom tag clouds. There are different methods. You can use a plugin or write your own code.

There is actually a function in WP for generating tag clouds. Here is some info in the codex.
codex.wordpress.org/Function_Reference/wp_generate_tag_cloud
And a successful example.
wordpress.org/support/topic/tag-cloud-custom-post-types

You will also find several plugins on wordpress.org that may do exactly what you want. Check them out and let us know.
wordpress.org/extend/plugins/search.php?q=custom+tag+cloud

Cheers,
Ed