1) Well in a desktop, sometimes there are add in cards that plug into the motherboard that have certain functionality - for example, a video/graphics card, a sound card, an Ethernet card, etc. However, the majority of newer motherboards and laptop have Ethernet functionality built in - so it would be interesting for the Ethernet port to have "jiggled" loose from the motherboard.
2) You can disable it - just remember if you are in a place with no wireless and you have to use it to reenable it. I would go through Windows updates and look for any downloads for an ethernet controller and install them.
AJ