Whenever I have been approached with this sort of interface, my response has always been the same - let the browser control the scrolling. Users understand what browser scrollbars are and how they work (both horizontally and vertically). My research and testing has shown that when you have the main content section of a page (the search results in this case) scroll independently of the rest of the content, it confuses more users than it helps.
Contrary to your comment, I believe that the web page's scrollbars are more than enough of a cue that the page scrolls. It is a common interface element that any average web user is going to understand.
To make horizontal scrolling more obvious, you can follow the design paradigm that Microsoft has chosen with Windows Phone 7. If it looks like the content is being cut off, the user will understand that there is more to the right and will know to scroll that way to see it. In a typical website design, if your content is wider than the viewing window, you probably don't even have to do anything extra. If you've got a grid of results, with borders and/or alternating row colors, as long as those identifying characteristics go all the way to the edge of the browser window, even if the content happens to cut off (e.g. the current column happens to end right before the edge of the screen), that visual cue will help the user understand that there is more to see.