I use the hi-def. AV pack from microsoft with a set of philips gold plated component cables..there is no visible difference from monster to the AV pack with quality cables..there is a striking difference running the xbox in progressive scan..well worth the money..
also not all xbox games are 480p..there are a few that do not support progressive scan..kung fu chaos, hitman 2 and the thing are a few examples of games that only support 480i..check out
www.hdtvarcade.com for a list of games and resolutions available..