You cannot tell the 08/08 board by it's part number, it's a combination of checking the production date of the laptop it comes from, verifying it's still the original board, confirming the gpu date is within the range of other known original boards, and doing some serious testing to assure the gpu is strong. A well tested board including bios update (middleton) will range you from $99 (pre 08/08) to about $250 for a pristine 08/08 or later board.
If you're planning on shopping only by price then I must warn you that it's a mine field out there with all the boards that have previously failed as it would only take a few mins to take your failed board and get it to work for a few weeks, perhaps months if you're lucky and sell it to an unsuspecting buyer. This is why the reputable sellers always do extensive stress testing on nVidia boards before they are sold.
If you want an inexpensive solution I have some factory sealed T60 boards with discrete ATI graphics that will fit your laptop with addition of a few small parts and some minor modification and they are only $29, or I could also source you an Intel board. If you'd like my help you can feel free to send me a PM and if you want to see a comprehensive list of all T61 boards you can check the table I made at...
http://t61.wikispaces.com/home#motherboards
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