Nat Geo Wild does offer an HD feed, D* doesn't list it on their list of upcoming channels though, they probably will carry it eventually. TomCat got the difference perfectly, Nat Geo Wild is more about animals in nature in the raw. The Nat Geo Wild channel brand has been around internationally for a few years now and it's great, I used to get the European feed online.
For those who don't know, Fox Cable, who distributes Nat Geo in the USA, actually discontinued original programming on Fox Reality back at the end of March and suggested providers start carrying the Nat Geo Wild, whcih launched the same day instead, which most providers except DirecTV and some others did. They kept the Fox Reality going on with repeat programming for them though the end of June when they officially discontinued the feed, which is why Fox Reality is now gone and Nat Geo Wild is here, except DirecTV put it in a more logical slot next to Animal Planet instead of Fox Reality's slot like most other providers did, which is why NASA was moved from 283 to 289 a few weeks ago. (Although they might have to move NASA again at the end of the year to make room right next to the Disney Channels for Disney Junior, which is replacing SOAPnet in 2011)