My postal code is listed as 100000 on a legit government site, however on my contract it's listed as 100007, so I'm not sure. Apparently if you mail to 100000, it should be completely fine, since it's the general code for Beijing. I've checked on government websites and gotten many, many different codes for my district, which isn't large, so I'm baffled. So, for now, hold off on mailing until I figure this out for sure.
Isa - Sorry about any possible issues, but I'm sure I'll get your post card. I think it's close enough, you have the rest of my address correct and the post offices really work here. My complex, street and district are all clearly named. Lets use it as a test, anyway.
However, there is more postal drama as my "mail key" actually doesn't fit at all in the key slot on my mail box. So many little issues...
On another note, if you haven't read BBC's Changing China series, it's a must. Especially interesting is the article on China's "brain drain," a tremendous problem that will affect the future generation.