At 4PM PST (7PM EST), the US producers of Gran Tursimo will be available to chat with on the PlayStation Boards. You will need an account with PlayStation in order to participate. You'll be able to ask hard-hitting questions like "how awesome is your game?" and "boxers or briefs?"
Gran Turismo 5 Prologue will be available at retail stores tomorrow, and on the PLAYSTATION Store this Thursday.