Here's a trailer from the DiRT Showdown demo which is now available on Xbox Live Marketplace, the PlayStation Network and on Steam for the PC. It apparently does contain both single player and multi-player content. The finished game is expected to ship on May 25th.

In the demo, the single player '8 Ball’ race, players take part in a chaotic, full-impact race in the shadow of San Francisco’s Golden Gate Bridge, using boost to sprint ahead of rivals and speeding through crossover points where drivers can dodge or takedown opponents. Once players have completed the race, they can challenge a friend online to unlock the 'Rampage’ multiplayer mode. In 'Rampage’, eight drivers feed their appetite for destruction in an online demolition derby event, earning points for crashes, smashes and eliminations.