Wal-Mart touched off a DVD price war on Friday when it announced a special pre-release price of $10 for many soon-to-be-released titles, including Terminator: Salvation, Angels & Demons, Julie & Julia, and Star Trek. Target quickly followed suit, adding such blockbusters as Harry Potter and the Half-Blood Prince, G Force, and Night at the Museum: Battle of the Smithsonian. Amazon then joined the fray, and Best Buy was expected to do so as early as today (Monday). Each of the retailers cautioned that the $10 deals were only available via their websites for advance purchases and only until the DVDs are officially released.