did you try what i said with the modem connected to your laptop then the ethnet cable going straight from your laptop to the xbox

if not try plugging it straight from your modem into your xbox via ethent cable i know this means you wount be able to surf while playing but handy if u just wana get on xbl asap.

does your internet service provider derinatly support xbox live, i had the xbox live starter kit for a yer because aol silver didnt support it lol.