I do have a multiple O-A visa that expires March 09. I plan to re-enter Thialand, October 08. Will I be able to obtain an additional year till October 09 ?

You might check with the consulate that issued the visa to see about getting a new stamp in your new passport since you can't do it here.

There should be no need for a "new stamp".

Just present your old passport with the visa, along with the new one

when you enter Thailand.

I do not know how the US "cancels" old passports?

At the British Embassy they cut the corner off the pages,

but are careful not to cancel pages containing current Thai Visas.

Just check the page with your O-A visa does not have CANCELED

or something similar stamped across it.

I understand it won't be a problem.

It would be a matter of having to keep track of 2 passports and dealing with immigration every time you make your 90 reports and etc. for the life of the visa.

If I had a choice and could get it transfered I would.

I have never heard of any procedure for transferring a VISA from one passport to another.

You would have to apply for a new visa from the Embassy with all the associated paperwork.

Immigration only transfers your current status, entry stamp.