There are several ways in which you can achieve what you want:
# Have your page made up of different parts which will update asynchronously according to the selected choice of the users. You will need to implement a decent amount of javascript for this so use jQuery for cross browser reliability. Also your website is data driven so using a good javascript mvc framework would be a big win.
If you have time you can view one of these:
AngularJS
Knockout
# Use master and content pages, have a common content page and update its data based on the category selected.
See this to create content pages if you don't know already.
Link
# You can even create a separate aspx page to show the category data and use an iframe to display that page, but this is my least favourite because I have seen iframes causing many problems on mobile devices and you wouldn't like that.