The Hordes rules will be updated after Warmachine's.
WM MkII is set to release in January, and around that time
PP will start the Hordes Field Test. Sometime after that, Hordes MkII will be released, probably at Gencon Indy 2010.
If I were to answer your second question truthfully, no, this is not a good time to start Hordes. However, there is still a way to start without shelling out for a rulebook that you'll just have to repurchase in a year. The starter boxes include a set of Quick Start rules (also found
here). They should be all you need to get familiar with the game system. Since the QS rules don't include infantry or solos, you'll be restricted to warlocks and warbeasts (They call these Tooth and Claw armies), but you can still expand by purchasing more of either if you choose.
A couple of notes about
WM/H and the upcoming rules changes:
1) Remember, the rules for each model are included when you purchase said model. You won't need Primal unless you want to use infantry and solos. You'll be restricted to Tooth and Claw until you pick up Primal or they release the MkII Field Test rules.
2) Most of the core rules are NOT changing in MkII. In fact, most of the changes will be made with the models' rules themselves. In
40k terms, this is nothing like the jump from 2nd to 3rd edition. It's more like going from 3rd to 4th with all factions getting a new codex at once.
3) No models will be made obsolete! All models in the current range will be represented somehow in MkII and they will fill a similar combat role. The balance might shift on a few things, making some of your models sucky (or awesome), but everything will have rules.