Logging in to a secure area


A regular client has asked me to set up a "logging in" area which will lead to an online store.

The logging in area will only be useable by customers that he selects (potentially hundreds), he does not want just anybody to be able to register and gain access (strictly chosen customers only). I redesigned his website last year but I do not host it (I was only given the ftp details and uploaded the new website), I had no need to get to the control panel and never was given the details for it. (I have a feeling that his previous designer is still holding on to the control panel access details, I had to call her in order to get the ftp details when I was approached to redesign his website)

Anyway, my question is - how complicated is it to set up a secure logging in area? (providing MySQL is available on his control panel right?).

Also, apart from MySQL, will I need any other applications or programmes in order to have this logging in area work?

Any recommendations on decent shopping carts? (I am aware of Roman-cart and obviously PayPal)

Thanks, much appreciated.
update -

I have looked in to MySQL a little and from what I understand it will help me greatly
(it will even provide me with the "username/password" codes apparently) - Can somebody reassure me of this?

I have 1 MySQL database on my current hosting account so I will be playing about with that later to see how I get on.

I've been told that there is no limit to how many usernames I can put in the database which is reassuring.
If by some chance my client does not have MySQL available on his control panel then is there another way I can set up a logging in area?

(from what I understand most paid hosting accounts come with atleast 1 MySQL database so I'm sure this won't be an issue but I always like to be prepared).

Thanks again, much appreciated
Go for a hosted shopping cart which can be white labelled and link to it. MySQL is there to sit behind a Content Management System (CMS). You shouldn't be trying to maually inserts users into the database. What about user management, user registration, blocking users, removing users, allowing users to edit their details, password reminder functionality - you either need a CMS to handle this or let the hosted shopping cart do it.