Hi,
Not sure if this will be any help or not, I did this trip in 2005 (before the olympics), I was told that I couldn't take any chinese money into the country (perhaps things have changed) and was advised to take US$. I took the equivalent of £500 cash in US$ and also £1000 in US$ on one of those american express pre paid cards (wouldn't advise this as it was difficult to unload it when I came back), others I went with took US$ travellers cheques, none of us had any problems changing it into Yuan when there, I had a great time and didn't even use the pre paid card.
regards,
Martin