[schakwin]

What you want to do is really easy. Whether it's right for you, only you can decide.
CP Notebook exports its notebooks into many formats. One of them is OPML, which stands for Outline Processor Markup Language. OmniOutliner opens OPML files readily and reads them as native OO files.
So, on a basic level, you export your notebook to your desktop as an OPML file and then open the file in OO and you will find your data and a sensible structure. You may have to fool with the structure to make it into what you want it to be, but it's basically there for you to work with. You save your file in OO format and there you have it.
I understand that you want your data in this format so you can use OmniFocus in some way that you didn't explain. That may be the best way - or the only way - to get what you want.
But, you need to realize (well, that's a little strong. Maybe better as "you might want to consider") that an OO outline, complex and wonderful as it can be, is actually a less "outlined" outline than a CP Notebook. The CP notebook can have outlines on its pages, each of which is comparable in complexity to a basic OO outline. The pages, in turn, can have each level and sub-level of their contents tagged with icons (another kind of outline), the pages, in turn, exist in an order (another level of outline) and can be separated by tabbed dividers (another level of outline).
And, of course, there are the famous CP indexes of words, tags, formattings, and so on.
So a CP notebook is really a collection of outlines many layers deep and extending over several conceptual dimensions. The OO outline, by comparison is a shallower, more limited structure.
This doesn't necessarily mean that the one is better than the other. A lawnmower is much more complex and multidimensional than a tablespoon, but I know which tool I would prefer to use to eat soup.
On the other hand, if you are using outlines designed to cut the grass and want to turn them into outlines designed as table utensils, you can expect to lose complexity and utility.
For many tasks, OO outlines are perfect, though I would love to be able to make the displayed typeface larger and to have cloning and tagging. For others, you need the extra depth of the CP meta-outline.
Good luck.

Stephen