I'm probably wrong, but I'm not sure you actually have an ethernet "hub". I suspect it is actually a "switch" or, in fact a 'router'. But if it really is a "hub" it's going to be half as fast as a switch, at best!
But, buying an AirPort because it is a 'router' is an expensive alternative, IMHO. I would only suggest a wireless connection if you want a wireless option. It will be handy, if you use the laptop in other parts of your of your house. But, for that convenience, you will also pay a price by having a slower and sometimes spotty connection. Wires are always faster, cheaper and less problematic.
And, since every thing is working now, there's no great urgency to change. Usually, each machine gets a copy of the DNS server info when it boots up, probably the same for the modem. If possible, get the cable companies actual IP address(es) for any servers they use and enter those numbers in the "DNS Servers" box in the Network Pref Panel.
