What I've done for clients in the past was to do a "save as" in my browser on their site (fully rendered design without the CMS specific variables), then I just cleared out the content data and replaced it with the XOOPS variables.
I think a few of the good designers have done some tutorials on this. In fact, Will_H just did a slicing guide. The Anatomy of the default theme will be helpful as well.
Stupidity is not a crime. Therefore, you are free to go.