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.