What is the correct way to book multi stop flights

I'm trying to book an UC round trip ticket, Outbound LHR-Tokyo, Inbound LAX-LHR for May 2010. However the Virgin website shows a figure of 5450. However, OPODO shows the same journey for 2750. It almost seems as if the VS website is taking my round trip as 2 one way trips and adding the two costs together. Am I doing something wrong on the VS website or is there a special we are meant to book multi-stop flights?
I also noticed that when trying to book the flight the VS website doesn't give me the option of booking a Limo as it usually does with UC bookings. What gives?
I also noticed that when trying to book the flight the VS website doesn't give me the option of booking a Limo as it usually does with UC bookings. What gives?