Hi
I didn't change CB in the end
I used Chrono Forms to just build a form to upload CV within the site (not at registration)
The form uploads the file to server and adds a value like
www.sitename.com/uploads/resumes/filename.doc|*|view cv to a CB field of type web address. If you set webaddress field to HYPERTEXT and URL then the value above causes you to just see "View CV" when vieing the field in profile or userlists and when click it links to the file in a new browser window.
I placed the field in a new TAB thats only visible to Managers and above so other users cant see each others CVs.
If you want to have CV file upload on registration then you have two options:
1) Build your own CB reg form using Chrono Forms (see their forums)
2) Build your own CB field type/plugin (much like the avatar upload) to handle files.
Good luck
Jonathan