You can play against computer(s) now. Thought I'd start a new thread since it has evolved.

To recap:

1. Download the beta client here (1.64 GB)
2. Install it and update to the latest patch (automatically)
3. Download the loader here
4. Get maps with AI in them here

All this information/the team working on this stuff comes from http://darkblizz.org/Forum2/index.php?board=96.0

One last caveat: The AI so far isn't very smart.