Firstly, great work with the plugin so far!
I'm running the latest version of WordPress from the trunk (currently 2.3-alpha). I'm aware that alphas are considered unstable, but since the introduction of the tagging system to the core... the current release of your plugin breaks with the categories.
I hacked around (slightly) with your code... here's a diff/patch of the changes I made:
http://wordpress.pastebin.ca/646960
I tried to make it backwards compliant - it should work with the WP 2.0 branch - but I haven't actually tested it myself.
Let me know what you think.
Cheers,
- Lee
PS. I also had a major problem with the installation of CWP, but it was related to a WP-bug with the register_activation_hook on Windows; (more info on trac). So I had to create the db tables manually! :-$