Although I have some experience with web programming, I am totally new to zencart and I have some questions.

I did do a search for this, but could not find the answer or a direct link to the answer (although people seemed to hint that it was possible)
How do you limit some products to only certain users?

Also, I already have a site with registered users. I want to port all of my users into the zencart user database, but zencart has some user requirement info (such as address and zip code) that I do not have on my users. Assuming I transfer all of the accounts with some missing information, when a user logs in to purchase an item, will zencart ask the user to fill in the additional information or will zencart just assume that since the user is registered that all of the necessary information is already entered?