What is the advantage of Dual-Band Wireless?
802.11b and 802.11g both use the same frequency band, 2.4Ghz. 802.11n can also use the 5Ghz frequency band. By using this area as well as 2.4 you get more available channels, so potential for less interference. Also in the 5Ghz band 802.11n uses channels which are twice as large, which increases the speed.
Therefore a dual-band wireless router, which is 802.11n enabled, will give you faster bandwidth, less interference, and better reliability.