How do I go about duplicating the default theme from MOSS 2007 so I can create a custom theme based on it?

It does not exist in the "THEMES" directory.

I've tried to copy and modify the core.css file to a new theme but some parts are messed up (black boxes, wrong text colours, etc)

Does anyone have a duplicate of the default theme as a standalone theme so I can modify it?

Or any other suggestions?

Thanks in advance.