Found the following post from a MS support tech on another networking forum, which may help fix your problem.
"Network stacking in Windows 7 was rewritten, and it is different from Windows XP. A network connection established over one interface will not tear itself down, even after a faster interface has been identified.
Only one interface can be used at a time, either wired or wireless. That means the current interface must be disabled, the other interface enabled, and the computer rebooted in order to use the other interface."
Thus, in order to used the wired adapter to connect to the Internet, you must enable the wired adapter and disable the wireless adapter in Network and Sharing Center, and reboot.
Note: Checking the Automatic Metric option in Advanced TCP/IP Settings for TCP/IPv4 will automatically select the network adapter with the fastest connection speed only if "Obtain an IP address automatically" is not selected.