iMac logic board part number

I have a 2GHz, Core 2 Duo, Intel, iMac 17" and I think the graphics card is failing.

I'm getting horizontal lines as well as windows freezing in places. I've looked around and I know I can't replace jsut the graphics card, I'm trying to locate a part number for my specific logic board but am having trouble. I can only seem to find boards for sale where people state the processor speed as the main description.

I have just fixed my vertical line issue by replacing my screen LM171w02 (TL) (B2) and don't wan't to add a new logic board that won't be compatible with my new screen!!!!

Please help me locate the part number