Half-Life Modem Play

Adapters and Protocols:

Go to My Computer - Control Panel - Network

If there is no dial-up adapter listed (as below), click Add, and go to Adapter - Microsoft - Dial-up Adapter.

If you want to play games that use the IPX protocol (as well as games that use TCP/IP), click Add, and go to Protocol - Microsoft - IPX/SPX.

After that, things should look something similar to this.

If you are not going to run a server, you should now click OK, restart the computer when asked to, and skip to the next section. If you are going to run a server, continue down the page.
 

Double-click on the Dial-Up Adapter.
In the Driver Type tab, "Enhanced Mode (32bit and 16bit)..." should be selected.
In the Bindings tab, only TCP/IP should be checked, or, if you want to play games that use the IPX protocol, IPX/SPX should be checked too.
In the Advanced tab, Use IPX Header Compression should be Off.
 

Click OK, then double-click the TCP/IP protocol.
Nothing should be checked in the Bindings tab (security reasons).
Nothing should be checked in the NetBIOS tab.

In the IP Address tab, Obtain an IP address automatically should be selected.

Click OK, and restart the computer when asked to.