Blockbuster is trialing rentals of both Blu-ray and HD DVD in the US. Titles will be available at just 250 select stores, and the company says it will hold around 40 titles in each format. Prices will match regular DVD rentals. There will be no surcharge for HD.Until now, Blockbuster has only offered HD disc rentals via its online operation. According to store spokesman Randy Hargrove, the move is an experiment to monitor consumer interest in the new systems.