I'm looking for a simple way to achieve search filtering like this : http://ckclinical.co.uk/search/
They are obviously pointing people to a empty search and then filtering by category. I've spent hours running round in circles :) Thanks.
Search is a big topic and therefore I can only guess the direction you want to go to. Like @MikeSchinkel in his comment was asking for more, I can for the moment only provide a list of links of which one might come close to what you need: