Okay, normally to connect to Xbox Live on a 360, you need to either use an ethernet cable and a wireless router,or you can spend about $100 for an overpriced wireless adapter that plugs into the 360's usb port. Neither sound very good. If your laptop or pc, however, are close to your 360, you can connect to live via the supplied ethernet cable.
Step 1) Connect your xbox 360 to a COMPUTER OR LAPTOP
Step 2) Go to the NETWORK AND SHARING CENTER
Step 3) On the left margin, click on MANAGE NETWORK CONNECTIONS
Step 4) Right Click on WIRELESS NETWORK CONNECTION AND CLICK PROPERTIES
Step 5) Click on the SHARING TAB and make sure BOTH BOXES ARE CHECKED
Step 6) Create or recover your gamertag and sign in to xbox live with your new internet connection.
Now you're done! I know step 6 was pretty obvious but i figured that i'd say it anyway.