If you want to test if your drivers are working - run glxgears. If you don't get spinning gears, chances are, it isn't working. If you do, chances are, they are working.
I think you need to restart X to be sure the drivers are being used - CTRL ALT BACKSPACE should do this, as will logging out and back in. MAKE SURE YOU SAVED WHATEVER YOU WERE WORKING ON FIRST!
Personally I use nvidia graphics cards as the support for them is excellent, but I've heard ati cards are well supported also.