Thanks for the replies, I will definitely take a look at that book, I'll either order a copy or cycle down to my library. As far as the database size goes, it'll be about 10'000 rows, as far as data size, it'll mostly be quite small, probably about five or six columns, with mostly short text (categories, names), there might be one big column of text, but even so that cell won't contain more than about 300 words.
I'm not sure about concurrent users. It shouldn't be more than say, 500 but that could be a severe underestimate. At this stage I'm not sure.