dont think of it like doubling your bandwidth as much as it is adding a 3rd wheel to a bicycle... you get a different IP on the nic and unless you get some teaming software (in which case it still might not work since they might have to be the same chip) you wont get any traffic going over one of the nics
even if you could team your nic's you wouldn't gain any speed unless what you connect to (and the whole path in between) is capable of more bandwidth. Ie - if you''re looking for faster internet nothing you can do will magically make your cable modem deliver it any faster.
Handy if you want to do something like network rendering to another tower with one nic while using the other for internet out
or use tower as a router/firewall for another tower etc
but will not increase speed