It's been years and years since I did any kind of search like this, though seeing how there are many experts on Yamaha's trail bikes here I'll ask away
does anyone have any info about this VIN number from a Japanese bike.  I am currently in negociation with the owner but he says he doesnt know the year
he told me the number 2NO - 002***

(would it be better if I posted this in the post 1977 section ?  As I am guessing this is a bike from around 78 ?)

You guessed right. 2N0 is the prefix for a Japanese Domestic Market DT125 from 1977 to 1980.

I would guess if it has a tubular black painted swingarm, it is 77 - 79 and if it has a square section painted silver, it is 1980.
Most common bodywork colour appears to be yellow.

Probably 1978, as you suggested.

The large document in the link below is not complete, but can prove useful.

Vintage Yamaha Enduro Fans - YAMAHA Model index -1958 - 2010 (yamaha-enduros.com)

Cheers, looks like I may be able to see it in a few weeks time,, will keep you posted.