First of all, Dallas is NOT a threat to the Lakers. They are historical chokers - They've choked so many times, and in the most monumental ways, too. Last year vs. Spurs in the first round, in the first round against the 8th seed Warriors when they won 67 games, and lost when they were up 2-0 on the Heat. Analysts love to hype them up, but they're not legit.
The threats I see to the Lakers this year are Houston and Oklahoma, and to a slightly lesser extent, Portland and Denver.
Houston: Pau has problems against Yao, so do a lot of the other Lakers (obviously lots of teams do, as well). Not only that, but Houston's front line is excellent. I'm very high on Scola and Mike Miller for them. Even with Bynum, their front line matches up well with ours. Aaron Brooks is really tough for Fisher, even Blake, but less so. Kevin Martin is just a stud. The guy can flat out score. Not that high on Shane, but he's ok. They also have a decent bench.
Oklahoma: I still think the Lakers have an obvious advantage against them on the front line. Russell Westbrook is an awesome and lightning fast player. Kevin Durant is a superstar, and Artest can only do so much. Also, OKC is a very long team, and they are tough at home.