Inspiron 1520 System Board

I have two questions, as it appears I need to replace the system board. The warranty on the laptop expired a week ago (just my luck).

1) How do I determine which system board is required for a system. My experience suggests there may be multiple system boards depending on the model.

2) Is there a way to order a system board from Dell, or do I have to take my chances on eBay or something similar?