How do I replace my wireless network card?

I have Inspiron 640M/E1405 which purchased two years ago. Recently my network card is dead, so I need to replace my card. I tried to find exact model but couldn't find it. Does anyone knows where I can buy it?

or Can I replace with other model of the card?

Below is the part number and description I have, how come there is two? 

Thanks for reading this and I'll be greatly appreciate your answer.

part number  Description

NC293          Card (Circuit) Network, Minicard, 3945ULD, MOW1

PF234           Module, Card (Circuit), Minicard, 3945ULD, Dell Americas organization

From Canada