I just wanted to thank you for your pictures and explanation -- they were really useful!
My wife just called me on her cellphone with the "flat tyre" indication, and rather than waiting for someone to come change the flat tire, she decided to change it herself (my wife's actually very good with mechanical bits). Following your step-by-step instructions and photos I guided her through the process over the phone. It only took about 20 minutes.
So your instructions let me be a "virtual OnStar advisor" today. Again, my wife and I thank you.
P.S. I haven't seen it yet (I'm still at work), but my wife found the cause of the flat was a big nail in the sidewall -- I guess we'll see if it can be repaired.
The only strange thing about this episode was that after the "Flat Tyre" indication, the system showed all 5 tires (including the spare) indicating the yellow warning trianges. My wife had to look at the tires to figure out which one was flat (it was obvious).