Microsoft have let loose the GTA IV theme and picture pack for Xbox 360 owners. Good news is that both are completely free to download!
Just go to your Marketplace blade -> New Arrivals -> Grand Theft Auto IV ... and there they are.
I don't have my capture card set up, but I just snapped a few photos of what they look like, apologies for the poor quality but see my flickr photostream for: picture pack
, guide button
, xbox live blade
, games blade
, media blade
and system blade