You can tour fine on that bike. You will be looking to add a rear rack, change the tires for something slicker, and fix some mudguards. You *might* also add bar-ends, have a new back wheel built, add a front rack, change the forks to rigid ones, and maybe one or two other things, but these are less important and depend on your budget. If you start on the optionals, you might as well consider gettting a new bike....from a cost and effort point of view. But then again the effort you put into pimping out your MTB will pay off in terms of how well you know your bike if you have mechanicals.
As crankarm says, questions like what is the best cheap tourer, can you tour on a mountain bike, etc., have been covered many times and it's well worth having a play searching the forum archives.