I have a permission to stay stamp untill January 2010,If i leave the country and have a re entry permit is the re entry stamp up to the original permission to stay stamp of january 2010 when i arrive at immigration at the airport.

Yes your permit to stay will be the same.

...I went through this process recently, I made a point of showing the details to the immigration officer on arrival at the airport when I returned and said the date that I expected to be stamped in until, best way to ensure that when you check your passport before walking away that there are no surprises that need to be 'corrected'.

Yes, VERY IMPORTANT that YOU check the date stamped in on arrival!

Happened to me, did not check and got my one year extension of stay reduced to 30 days entry!

Had to go to Soi Suan Plu - but they did help me with a smile and everyone uttered "no ploblem, no ploblem" and fixed it!

Many thanks for the replies i will do as is suggested