To configure a default gateway:
Open Network Connections
Click the local area connection you want to configure, and then, under Network Tasks, click Change settings of this connection.
On the General tab, in This connection uses the following items, click Internet Protocol (TCP/IP), and then click Properties.
On the Alternate Configuration tab, click User configured. Type the values for the IP address, subnet mask, and default gateway.
To open Network Connections, click Start, click Control Panel, click Network and Internet Connections, and then click Network Connections.
If you currently have TCP/IP configured to obtain an IP address automatically, you must manually configure a TCP/IP address and subnet mask in order to configure a default gateway.