There is no difference between the Network and Ethernet card, they are both names for one and the same thing, a Network Interface Card. Ethernet just specifies which type of media used. Read
this guide for more.
The 10/100Mbit part means that the card can switch between 10Mbit and 100Mbit, the speed at which the network runs. So you can use this card for ADSL (which needs up to 10Mbit) or for a Local Area Network (LAN) at 100Mbit. Do know that the speeds are set in bits per second, to get to the throughput speed in kilobytes per second, you divide the number by 8, as there are 8 bits to a byte.