Is that going to end up being a static site? Unless they're just looking for a graphics/webpage designer, I'd do somethign interactive to show that you can program AND make nice looking pages.
I don't know what these people you're interviewing are looking for, but if it were me interviewing for the job I'd build something that the company itself would find useful. Like an app for their hr department to manage info on their employees or a calendar app for their salespeople to track their sales and time or an inventory database over the web that the user can add items, delete items, modify items and query and prints out reports.
I'd put it all together and propose an intranet site if they don't already have one, and if they do you say you thought your app(s) would make a good addition to their current intranet.
Something they can look at and say "we need something like this".
If you already work for the company and are trying to get into the IT dept then you can probably identify some problems the company has that your web skills can solve. If you're trying to solve problems within the company before you even have the job I think it shows you're a go-getter with some hussle and they'll like that.
