Well it is possible, but for a one week stay and assuming you were not going to stop along the way, it would be the slowest and most expensive method.
From KL the route would be something like train to Bangkok, then bus or train to the Cambodian border, then bus to Siem Reap, then to Phnom Penh then to Saigon. To do this would take (roughly) 4 days (depending on overnight stops and connections.
Alternatively AirAsia flies KL to Saigon direct for around US$50 and the flight takes 55 minutes.
#2somtam2000 has been a member since 21/1/2004. Location: Indonesia. Posts: 8,065