You take 2 or 3 LA, basically you gain nothing for it but count as 2-3 levels higher for your xp level (and how much it takes to reach the next level) and wealth by level. For example, if you started as an afflicted (+2 LA) Werewolf Barbarian 4, you would be an 8th level character: 4 Barbarian levels, 2 "Wolf levels" and 2 LA. You would have only six hit dice (and thus 3 feats [HD 1, 3, and 6], and only one ability score adjustment, etc...), but would have level 8 xp and money. In order to get your 7th HD, you'd need to get 9th level xp, and so on. The animal HD are like class HD, you get hit points, skill points (only 2 + int from a poor list, though), and if it's your 3rd HD a feat, and if it's your 4th HD, ability score +1.
Usually you take racial HD "first" since you know..you can't be a Fighter before you're a Minotaur or whatever. Lycanthropy is unique because you can acquire it after adventuring for a while, so you need to have at least one class level HD before you can take the template.