Half-Life Modem Play

Starting a Server:

If you're only going to be connecting to servers, not hosting them, go to the next section.
 

Go to My Computer - Dial-Up Networking, and select Connections then Dial-Up Server (as below).

Select Allow Caller Access (note that while this is on, the computer will answer any call that comes in, so make sure to turn it off later).
Click Server Type. Type of Dial-up Server should "PPP: Internet <etc>", as below. Enable Software Compression should not be checked.
I think that Require Encrypted Password doesn't really alter anything important, but can cause problems (as far as I know, if you set a password, the password is required whether Require Encrypted Password is checked or not). Not sure though.

If you want to set a password, click Change Password, leave the Old Password field blank (unless you've set a password before. In that case, enter the old password), and enter the new password in both of the fields below.

It's not usually necessary to set a password, no1 is likely to know to dial that number just then unless you tell them about it, and even then if you have things set up right they shouldn't be able to do that much. Still, no harm in being careful (usually :)  ).

Click OK. Any calls on the line connected to your modem will be answered by the computer. There should be an icon like this:

Skip to the Starting a Game section for info on setting up a game after someone's connected to your server, or continue to the next page, Client Setup.