You can certainly use a network connection with a TiVo.
If I understand correctly you bought the 2nd TiVo with the network card already fitted. The question really is what state is the software in. Assuming it has not already been configured to use AltEPG you can follow the instructions here
You might have some issues with the network settings if your broadband router is setup differently. Hopefully the seller supplied you with some information about the network settings the TiVo currently has.