Subcategories was an off the cuff thought rather than a want, I tend to try to work things out as I type (call it cheap therapy). I'll take a look at those threads you suggest. As for why I want different themes and colours?
I am trying to build a review site - I haven't watched a film, read a book, played a game or even listened to a new album because if I do I start writing about it and if I do I need somewhere to post it. So with a review site, which I might persuade others to contribute to, I'd like a seperate css or theme. I think, in order to keep the feel of identity, I would prefer simply to change the colours of the CSS, changed the headers and change any icon images to another CSS rather than new templates etc.
Music would be one style, games would be another, film and books another. On top of this, there would be a main page which would pull the latest posts from each of the parent categories - ignore the child categories, as I will not be using them.
I worked out that if I could get a different style for each category, I only need a single installation, because the main front page should be able to pull the recent posts for each category - I assume that is. I also assume by taking the archive permalink for a category and using that as an actual link to the page, it would display the latest posts from that category.
There's lots I need to do, I just need quite a bit of help getting it done. I tried to change theme to style in the title as it seemed the core aim, but couldn't do it. I'll give those links a go, though I suspect I may have already tried some of them As for the Multi-User WP, the problem is...where's the support? It's a seperate entity really, and I prefer a WP jobbie from WP