Step -1
Download Cain and Zonealarm (In the downloads section)

Step -2
Open Zonealarm , from the left menu you should see and option called Firewall, Click that and you should see new options in the middle. Like main, Zones, Expert...Click Zones.

Step -3
you should see 2 already in there called " New Network " Just leave them there supposed to be there, you are going to need the xbox server before you do any kind of forcing or anything like that. So open Cain while your signed onto xbox live, and make sure it is searching for your ethernet adapter for your xbox and wait for the ips to come up there should only be like 2 or 3

Step -4
Once you have the xbox live ips go back to zonealarm , and click the add button at the bottom, and 4 options should come up
  a. Host/site
  b. ip address
  c. ip range
  d. subnet
Click ip address.

A new window should come up that has,
a drop down bar that has

-Trusted, and blocked
-Ip address
-description

keep it as Trusted, in ip address put in the xbox live ip address, and put anything for description( i just put xbox live) then click ok,( do that for all the ips that came up in Cain)

Step -6
  a. Have the person you want to force host to, to go make a party, and have no one else join
  b.Use Cain to get his ip
  c.Put his ip in the trusted zone of your zonealarm
  d.Click main, in Zonealarm and and it will ask you to save click yes, then       make sure your Internet Zone Security tab is on HIGH and your Trusted Zone Security is on Med.
There your friend should now be host!!