It's on the Wikitravel link I posted, along with other sites. (Scroll down to Get In / By Bus. It doesn't mention the transfer, but my friend did and I saw that somewhere else I think.

There is a transfer with the buses going from the Stadium. My friend and some others were dumped on the side of the road by the driver after his ticket was checked. New bus came along and took them to Zhunjiajiao. He was a bit stunned and had no idea what was happening, but it all worked out well. It's a two hour trip, and there is one bus going in the morning and one in the afternoon. Not something I want to do.

The Express bus from near People's Square runs every half hour, and is an express. That's the one to take. BTW, there aren't tours exactly. The bus (either one) gets you there, then you go to tourist office to arrange tours locally if that's what you want. You will have to pay something to see the sights like temples etc. There are also regular tour companies that shuttle you around for larger costs.

Any info on how often the trains run? I'd really be up for a more flexible schedule, like the Express bus or the train. That also means you don't have to take a bus to the Stadium. However, the buses from the stadium are cheaper than the Express bus - probably because they make more stops. They are listed at 2 CNY and up, and the Express bus is 12 CNY, obviously a first class kind of ride rather than economy!