Can anyone suggest a place to by a mountain bike in hanoi? I cannot find anything on interent.

I would be surprised if you could buy anything decent in Hanoi. I was there in 2000 and things may have changed but the only bikes i saw were pretty old fashioned styles. On the other hand, if you want to buy a motorbike, i am sure you will have no trouble.

Hi! Try looking on Pho Ba Trieu between Hoan Kiem lake and Lenine Park.... I just baught a fairly decent bike that I am planning on taking to Mongolia on a 3000 km journey through china in 2 days... after wich I will have a better idea of the quality!
Cheers,
Good luck!
Liel
Unless things have changed recently you cannot buy any reputable brands of mountain bike in Hanoi. Bangkok and Hong Kong are the only cities in that region where there are bike shops selling a decent range of reputable bikes. There are lots of 'lookalike' mtb's for sale, some may be usable, others are deathtraps. You really need to know your stuff to be able to tell the difference. I've seen tourists with serious injuries as a result of broken stems and cranks on locally made bikes. If at all possible, buy elsewhere or bring your own.
For Liel's sake I really hope I'm wrong about this!