Including Vietnam
 

Mrs Zandy and I are planning an RTW for autumn 2011 as holiday trip. We want to include a visit to Vietnam arriving in Hanoi (HAN) and leaving from Ho Chi Min City (SGN) with the journey between as a surface sector. We would be aiming to include both Hong Kong and Singapore on the route from LHR to Australia and beyond. My attempts with the OW RTW planning tool refuses to allow me to book HKJ/HAN, which from the sticky I now understand to disallowed on a RTW booking. I'm considering booking the Vietnam trip stand alone but would like to avoid the extra cost. Any ideas?

I think the FAQ Sticky is out of date with regard to the restriction on the CX HKG-HAN flight.
There is no longer any mention of this restriction in the fare rules
And I have just constructed an itinerary in the on-line tool that includes the flight (using the KA designation; KA operates the flight and CX codeshares on it); availability seemed low, even if booking a business class itinerary

An option is to get to HAN via NRT (or to leave HAN via NRT); JL has a daily flight

As pandaperth says, there USED TO be a restriction disallowing HKG-HAN, but that is no longer true.

There is a Dragonair (KA) flight HKG-HAN that is allowable under the RTW rules.
Only 1 flight per day on an A320 and depending on the day of the week, the times are different, so make sure you check that.

The JL flight is also daily and is a 767.

Those are the only two OW options to HAN at present.

FYI, JL will be using their latest regional C seats and IFE on NRT-HAN. You might want to try it out