I've been to Beijing more times than I can keep track of, though I've always had to squeeze my photography into the interstices between fits of working. As you'd expect, it's a great street-photography city; I also think the obvious tourist attractions (Forbidden City, Summer Palace, Great Wall...) are well worthwhile, even though I'm not usually a big fan of tourist attractions. In my opinion, the best photographic opportunities in the city, though, are in the residential back streets early in the morning while the city is waking up. There aren't a lot of the old "hutong" neighbourhoods left, and those that still exist are turning into tourist destinations in their own right, but if you can find one that isn't crowded with visitors they make great places for exploration.
Of the "standard" locales in the city, I think the Summer Palace has the nicest combination of scenery and architecture. You don't need a driver to get around in the city---the subway and the taxi systems are both excellent, although the taxis aren't as cheap as they used to be (before the Olympics, they forcibly retired the old generation of red taxis, which were tiny little rattletraps that smelled like they had 2-stroke motors---environmentally appalling but with a certain perverse charm). Beware of taxis *without* the official sticker, though---I've only taken one once, and it had the most creative meter I've ever seen (I think it was set to measure the distance in kilometres but compute the charge in miles, or something like that).
You need---ABSOLUTELY NEED---a card with the name of your hotel written in Chinese. The concierge desk will have them; if lost, you can show the card to a taxi driver and get taken home. Once you have that safety net, for heaven's sake go out and get lost!
Everyone goes to the Great Wall at Badaling and that's probably what your tour will do---be aware that (1) that section of the wall is a modern reconstruction, and (2) so what?---the wall has been built and demolished and rebuilt in sections all through its history. It's still a wall and it's still great. That said, the less "updated" sections have a good reputation, if you get a chance to go to one.
I loved Xi'an and spent a lot of time walking around the Muslim quarter and its associated night market. (I looked for interesting cameras but didn't find much; some junky old Seagull TLRs and Hongmei folders, but nothing good and not at bargain prices.) The wares are mostly tourist crud (near the Drum Tower) and everyday household goods (further away where the locals go), but the food is decent and the crowds very photographable. I ran into a few people who didn't want pictures taken, but it was always a civil interaction---obviously I avoided shots that seemed likely to give offence, though it broke my heart to miss the picture of the room full of old Hui men sitting down and singing together in what seemed to be a pre-evening-prayer ritual.
Personally, I'm not a big fan of zooms and would rather use a normal lens when possible, but everyone has their own taste in these things. (How fast is that 70-200? I had an f/4 lens at the terra cotta warriors, and it wasn't really fast enough.)