Looks like it's probably a no go..
I know that the border is apparently open a Sikkim (although apparently only for specially licensed traders from the region, but it looks like there is no way for foreigners to cross over the border. Alternatives seem to be to go through Pakistan (which is way too far for me - can't afford the guide all the way from there to Laos) or through Nepal into Tibet, which has its own problems - need to be part of a group, need a special permit, and may have difficulty getting from Tibet into the rest of China.
I'll probably end up going to Kathmandu, Kolkata, or Dhaka and shipping to Thailand by air. Bit of a bummer, I really wanted to go overland all the way
Oh well... this info is all from either the Lonely Planet forum or this one - no official word anywhere. If anyone know otherwise, please update me.
Edit: Thanks for the link, looks like you found it out before I did...
Last edited by gazlm; 30 May 2011 at 22:41.
Reason: Didn't read the above reply properly