Let's see if I can remember how I did it.....
First, you need to install IIS and the SMTP service. It'll probably ask you to restart. Do so. After it's installed, go the Administrative Tools, and then Services, and make sure the SMTP service is started. Then go to Admin Tools and choose Internet Services Manager. Expand your machine, and you should now see Default SMTP Virtual Server. Make sure it isn't stopped. Then, go into your email program, and change your SMTP server to "localhost". Then, all sent mail will be directed through your server. If you have a firewall, I suggest you set it to allow inbound connections from only "localhost". Ta da.