This week's additions to the WiiWare and Nintendo DSiWare downloadable game services offer fast cars, talented canines and classic casino kicks. Gamers can get behind the wheel of a world-class speedster in Need for Speed: Nitro-X or enjoy short- and long-distance running challenges with Triple Running Sports. If it's pet-oriented fun you're after, Derby Dogs lets Wii owners raise their own talented pups and train them for competition, while Go Fetch! gives Nintendo DSi users a way to give their virtual pooches an active workout. For a taste of Las Vegas anywhere you go, 21: Blackjack puts a high-stakes card table in the palm of your hand.