Per the bestiary:

For monsters with racial Hit Dice, the best way to allow monster PCs is to pick a CR and allow all of the players to make characters using monsters of that CR. Treat the monster's CR as its total class levels and allow the characters to multiclass into the core classes. Do not advance such monsters by adding Hit Dice. Monster PCs should only advance through classes.

If you are including a single monster character in a group of standard characters, make sure the group is of a level that is at least as high as the monster's CR. Treat the monster's CR as class levels when determining the monster PC's overall levels. For example, in a group of 6th-level characters, a minotaur (CR 4) would possess 2 levels of a core class, such as barbarian.

Note that in a mixed group, the value of racial Hit Dice and abilities diminish as a character gains levels. It is recommended that for every 3 levels gained by the group, the monster character should gain an extra level, received halfway between the 2nd and 3rd levels. Repeat this process a number of times equal to half the monster's CR, rounded down. Using the minotaur example, when the group is at a point between 6th and 7th level, the minotaur gains a level, and then again at 7th, making him a minotaur barbarian 4. This process repeats at 10th level, making him a minotaur barbarian 8 when the group reaches 10th level. From that point onward, he gains levels normally.

GMs should carefully consider any monster PCs in their groups. Some creatures are simply not suitable for play as PCs, due to their powers or role in the game. As monster characters progress, GMs should closely monitor whether such characters are disruptive or abusive to the rules and modify them as needed to improve play.

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So here is where the issue becomes...murky.  A werewolf has a CR of 1+ whatever else it had.  Per these rules, does it count as a CR 1?  In which case, can it never be bought off? (note the bit about round DOWN).

What about for a half-dragon? CR+3?  Does this character count as CR3 for these purposes?

Talking with JoeD got me thinking about these rules, since I know playing a werewolf is in his bucket list.

The werewolf would basically have 1 level of werewolf and then class levels through normal advancement. The rules as written would not allow for the werewolf character to have equal class levels to the party, however, I think it would be reasonable for a DM to grant said character the extra level at some point if the character was underpowered or the player felt they were falling behind.

As for the half dragon, I would use the CR+3 as its effective CR. The game is saying that when you make an NPC that is a half dragon, you have to add 3 to its CR to account for the power increase. I think that would apply to PCs aswell and the character would gain 1 extra level in between 3rd and 4th.

YAY! missing 3.5 templates at this point....

Were I remaking the game, I'd have added in races like these from teh get-go.  Made it WAAAAAY easier.

well, alternatively, you COULD just use 3.5 level adjustment templates as pathfinder was meant to be compatible, but it would have to be looked at and potentially rebalanced.