Merge two or more categories in a search

Hi you all. I’m creating a new site based on WP that will work as archive/portfolio for ad campaigns. Now, imagine that I’ll treat each campaign as a post. Then I’ll classify that post in several categories according to the product and the media channels where the campaign will appear. Imagine that the campaign will be in the radio, tv and newspapers. So I’ll classify that post in those 3 categories. Until here, no problem at all. Now, the user will need to use this kind of search: All the campaigns from product X (a category) used in Radio (another category) and TV (another one). How can I achieve this?

p.s. Sorry for my lousy English…