Having Windows prefer a wired connection is preferable in a number of situations: When your wired connection is faster, or your wired connection needs to be preferred because it’s a private LAN, etc.
As far as I am aware, there is not a way to completely disable the wireless adapter when an Ethernet connection is available, but you can have Windows prefer the Ethernet connection over the wireless, effectively doing the same thing.
To do this in Windows 7, do the following;
Open Control Panel, then Network and Sharing Center, click Change Adapter Settings, then tap the Alt key to show the menu. Click Advanced, then click Advanced Settings.
On the Adapters and Bindings tab, in the Connections pane, reorder the connections using the arrow keys, putting the most preferred (wired) connections on top. This will have Windows automatically prefer the wired connection over the wireless.