dunno if you know html, but it really isnt very tricky. If your client wants to add just text it should be simple for them to do. Essentially HTML is tags (such as <font> and </font>) which have text in between them. consequently it will be very easy for you to show the client how to update the text in between the tags that need updating. you could slap a bunch of comments before and after the updateable text (i.e.) <!-- edit the following bit --> this would make it easy to update. so long as you show the client how to save/upload files etc, and make the design so that it wont go horribly wrong when more data is added this shouldnt be a problem.
It is perfectly feasible to write a program that would allow the user to update a page, by using a cgi script, asp or php etc, much in the same way that this message board updates its pages with php. however, this would add a whole load of extra hassle, you would have to charge a fair bit more. (client probably wouldnt want this!)
and with the ecommerce situation, i am no expert here (i am about to learn asp myself!) you could go this route, and learn asp,php sql etc, or use third party software to handle this. (i am sure somebody here will be able to point you in the right direction). password protection wont be very tricky though, using a perl script and forms you would get the user input, and use a simple if statement to test whether the input matched the password. this type of script would be the type of thing that you can download very easily from the web.
I have a little proposition here. What your client wants (the ability to update his site himself without ever touching HTML) is something that I have been offering business, especially real estate agents, down here in Tulsa, OK. I would be lying to you to say that what you want to do is super easy. It is not that it is too hard, but it is time consuming, and many prevent you from making any deadline that you have with our client. Anyway, I don't normally go around soliciting people on the boards, but here is my proposition. I know C, Java, C++ and Perl programming, as well as being quite experienced with CGI and Database work. If you would like to sub-contract out the backend work, I know that I could give you and your client what you want. Another great plus is that the prices are lower down here in Oklahoma than in NY.As just a simple example of my programming skills, check out my footer bellow. I did it today, so I am very exited! It is run by a Perl CGI script and mySQL database.
Anyway, visit my site, and drop me an email. And don't forget, sign my micro-guest book bellow!