You can use Office Live Small Business to get this functionality for free -
and I am currently using that solution myself and can confirm it works
excellent.
Go to
http://smallbusiness.officelive.com/ and create an account (using your
existing Windows Live ID account - or you can set up a new Window Live ID if
you like).
Once there, go to the Business Applications section (which is basically the
SharePoint portion of your Office Live account) - you'll find it under the
'More' menu option in the top navigation bar.
The first time you click there, you'll be asked to wait while the Business
Applications feature is activated (a few minutes - basically, it's creating a
new SharePoint workspace).
You can then use the default 'Documents' document library in the default
Document Manager application - or alternatively, add a new application and/or
a new document library.
With the basic, free service, you can have up to 5 different users including
yourself. Each user login is based on an email address, but if that email
address doesn't already have a Live ID associated with it, that user will be
required to create one (and keep in mind you can create a Live ID for ANY
email address - not just the Microsoft ones ending in hotmail.com or
live.com). Also, your Business Applications area (ie, the SharePoint portion
of your Office Live Small Business account) allows you up to 50 MB of
storage.
You can upgrade either the storage or the number of users (or both) for a
*very* reasonable price - you'll see links to it in the associated areas - or
conversely, you can go to Add/Manage Services option in the top navbar's
'More' submenu.
To create a shared notebook in your document library of choice, make note of
its URL when you've navigated to it via clicking its tab in your business
application - and strip away the 'Forms/AllItems.aspx' at the end.
In OneNote, select to create a new notebook, choose a name and a template
(or use the blank template) and click Next. Then select 'Multiple people will
use this notebook' and 'On a server' radio buttons - and next once again. And
finally, enter the URL you've noted (once again, with 'Forms/AllItems.aspx'
stripped from its end) - make note of the full path URL being show right
below the URL text field - it's basically that same URL you pasted, with your
notebook's chosen name as the subdirectory - and this is what you'll give out
to other users (and what will appear in the email that's automatically
created for you to send out to your partners if you leave the checkbox below
checked when you hit 'Create').
Hope this helps. Let me know if you have any further questions,
Tom