You'll want to set the Metrics on each adapter.
This way your LAN is listed first on the routing table. The binding above will affect DNS queries, but you'll also want your routing table to choose the LAN's gateway first, before the Wifi's gateway.
Here is the relevant Microsoft technet article.
edit might as well cut and paste the instructions in case you can't find em.
You can change the interface metric on a network adapter if you are
using TCP/IP as a transport protocol because TCP/IP uses the interface
metric to determine the order. You can change the interface metric to
make one network adapter more favorable for all TCP/IP connections.
The interface metric (IPConnectionMetric) for a network connection
indicates the cost of using the routes in the IP routing table. The
routes are derived from the interface configuration. The cost becomes
the value in the Metric column for those routes in the IP routing
table. If there are multiple routes that are a close match for the
route to a destination in the IP routing table, the route that has the
lowest metric is used. The range of valid values is 1 through 9999.
To view the IP routing table, type route print at the command prompt.
For more information about the Automatic Metric feature that is used
in Windows XP for IP routes, click the following article number to
view the article in the Microsoft Knowledge Base: 299540 An
explanation of the Automatic Metric feature for Internet Protocol
routes To change the interface metric, follow these steps: Click
Start, click Run, type ncpa.cpl , and then click OK.
The available connections appear in the LAN and High-Speed Internet
section of the Network Connections window. Right-click the network
adapter that you want to change, click Properties, and then click the
General tab. In the This connection uses the following items box,
select Internet Protocol (TCP/IP). Then, click Properties. In the
Internet Protocol (TCP/IP) Properties dialog box, click the General
tab, and then click Advanced. On the IP Settings tab, click to clear
the Automatic metric check box. Then, type a value in the Interface