From the factory the Tit X had nice half leather heated seats, larger wheels, adaptive lights (the ones that move around corners), and push button start - but it appears that some non-X models have been spec'd up a bit, so some may have some of those too.

There should be no difference in price between them when you get to 08-09 cars, so if you can find an X you may as well get it, as they have all the toys. But if I was you I'd look for the Titanium X Sport - the 2.2 is a great engine, and the Sports look a lot nicer.

Would definitely recommend a diesel over the petrol - they're quicker, a lot more fuel efficient, and very reliable. Mine's on nearly 150K and has only needed routine maintenance.

Edit: Found brochure here