I suppose just an Ethernet port for internet?
if all you're doing with this is browsing the net, keep in mind the fastest internet available from time warner cable in NYC is 50Mb/s. (and that's a $30 premium over their standard service)
their standard service is 15Mb/s.
if you've got DSL you're probably slower.
if you've got Fiber to the home (like FIOS) you're probably faster.
so the 100Mb USB adapter will be more than enough.
if you're wireless N, that is faster than 50Mb/s. (and probably faster than 100Mb/s if you've got a good signal)
wireless G is also probably faster than the standard level from time warner.
*if you alt-click the wifi icon in your menu bar, the "transmit rate" is the speed of your connection, see how that number compares to what you're supposed to be getting from your net provider. if they are close you probably won't see much speed increase.
** i keep saying probably, because there are a lot of variables that affect wireless, so speeds seen by you may not match others, or even if you move from one side of the room to another.
the only time you'll see a noticeable difference in speeds is moving files around your network, so to another computer, or to a back up device like a time capsule.