Your good to go. Just have your comp and Xbox hooked up to the same router. go to XBconnect.com download all the stuff you need (The latest XBC version and some other stupid program I forgot the name of but it tells you on the site.), make sure you have no viruses/spyware/adware on your comp. Turn on your halo and leave it at the join game screen and launch XBC.
Once your XBC is up click on the "Find" menu at the top of the screen and click "Find My Xbox" (the second program you dl is what is used to find the XBox), once it's found just host or join a game.
Blam! it's like halo on Xbox Live.