It has since been confirmed in a Tweet by Bethesda Softworks: ”Dawnguard will be out Tuesday for 360 in English. FIGS 1.6 patch for 360 coming next week and Dawnguard FIGS will be out mid-July.”
FIGS stands for “French, Italian, German, Spanish.”
Dawnguard will be available on Xbox Live for 1,600 Microsoft Points or PSN/PC download for $20