Originally Posted by virtualtroy
I'll be in Beijing this October but only for 1 day

Arriving into PEK? When does your flight depart? I assume you have your single or multiple entry visa secured?
It doesn't take long to clear PEK Border Control (maybe 30 minutes from stepping out of jetway to landside in the terminal). I last went in 2001 so I can't remember the complete series of steps, but it took very little time, there were probably 15 or more lines open in Border Control, with only 4 or 5 people in each non-chinese line. Out of Border Control you go down the escalator to the right, down to baggage claim, then get your bags cleared and out into the landside area of the terminal.
You'd be well advised to either have some ground transportation arranged ahead of time, or go OUTSIDE to the taxi stands to get transportation. Hustlers will hit you up the moment you step into the landside arrivals part, offering you a cab ride downtown for 450 RMB, way over the going rate (should only be 70-80 RMB if memory serves). These are what you would call gypsy cabs.
Originally Posted by virtualtroy
Is it realistic to assume that I'll be able to visit both a section of the Great Wall (any suggestions which part and how far it is from the city?) as well as the Forbidden City?
I seem to remember that PEK airport is about 30-45 minutes by cab to "central" Beijing (Forbidden City, Tienanmen Square, Great Hall of the People, Wangfujing shopping street). I can't remember the direction the airport is from the central city, but I do know that the closest and most popular section of the Great Wall, Badaling, is 45-60 minutes northwest of central Beijing. All this depends on time of day, of course, expect New York City or worse gridlock/traffic on typical morning/afternoon rush hours. On the other hand, there are thousands of 'red cabs' available most anytime on the street, among the ever-increasing throngs of private automobiles. And, it seems there are even more bicycles, they are everywhere are they will dart out in front of vehicles without hesitation. However, I digress...
Forbidden City should be given at minimum a few hours and at best half the day. Tienanmen Square is huge and is great for just walking and people watching.
Another thing to note, the first week in October is typically a national holiday week (I think Chinese "National Day" is October 1). I was in Beijing Oct 1-5, 2001, and being in the Square among 500,000 Chinese people, enjoying the amazing fountains, was definitely a trip to remember.
You might be able to go right from the airport to Badaling to see the wall, allow 3-4 hours round trip to walk up and back and enjoy the view, then get into central Beijing and enjoy the square in the evening at sunset (with all the smog - or at least back the smog back in 2001 - the sunsets are incredibly orange). Then hopefully your flight leaves the next morning. If it leaves late same day, you will be time crunched for sure.
I hope this helps.
Jim in Nebraska