Let me deal with the ethical question, though, putting aside the epistemological and scientific questions (particularly whether we can learn as much or more without resorting to vivisection). I've been meaning to scrawl a few thoughts about animals for some time now.
I'll make three assumptions just to make the topic manageable in a single blog post. First is that animals are not the same as people. Second is that a right is a kind of claim. Third is that obligations stems from the overwhelming weight of reasons. I'll explain these in turn.
It should be evident that biologically, animals are not the same as people. Even higher primates such as chimps are not the same as us -- only very, very close. But the point is not biological, but moral, in that animals do not have the same moral status as people. "Moral status" is a term of art that I take to refer in part to the moral capacities of a creature, and in part to the moral value of a creature. (There may be more to it, but these are the essential features.) Moral capacities include the ability to morally deliberate, to recognize moral obligations and rights, and to make moral decisions. Moral value is, I take it, a primitive property that can be possessed by anything. So, in saying that animals do not have the same moral status as people I am not saying that they necessarily differ in moral value. (Indeed, there's an argument to be made that most non-human mammals are more morally valuable than Ted Bundy or Clifford Olsen.) I am saying that animals lack particular moral capacities. In particular, animals lack our ability to recognize moral obligations and rights. (Keep in mind that I am only explaining an assumption, not arguing for a claim.)
When I say that a right is a claim, I am overlooking a lot of potential rights -- for example, the right to sign contracts. The right to sign contracts is a power that one has, not a claim that one makes (against someone else). However, it's a simplifying assumption to only deal with rights as claims, as most rights fall into this pattern. The right to free association is a claim against the state such that the state cannot interfere with one's choice of companions. Similarly, the right to freedom of speech is a claim against the state such that the state cannot interfere with what one says. And so on.
Finally, I am assuming that obligations arise due to the overwhelming weight of reasons. There can be reasons for and against any given course of action. Indeed, it is a rare course of action that has nothing to be said both for and against doing it. These reasons may have differing weights. For example, if I am trying to decide whether to keep my promise to meet my wife for lunch or to offer assistance to a seriously-injured man at the roadside, the reason afforded by my promise has lesser weight than the reason afforded by the stranger's immediate need. In some cases, it may be that the weight of reasons tilting one way or the other is not extreme -- that is, although one has more reason to do X rather than Y, one still regrets not doing Y, and, indeed, could understand why someone might choose to do Y rather than X. This would be a case of non-obligation. A case of obligation to X, by contrast, would be a case in which one has overwhelming reason to X rather than Y, and one would fault choosing to Y rather than X.
Given that, what should be said about vivisection? The first, of course, is that animals do not have rights. Animals lack the ability to recognize moral obligations and rights, and hence lack the ability to make rights-claims. Thus, animals have no rights. (Yes, I've basically purchased this result by definitional fiat.)
The interesting question, though, is whether we have obligations towards animals. Of course, we do. For one, we can acquire these obligations by promising -- when we purchase pets, we are promising that we will care for these animals. We can also acquire these obligations collectively because the situation the animals find themselves in was caused by our collective action. If we destroy an animal's habitat, we acquire reason to provide a new habitat or otherwise make good on our error. The underlying reason for all this is that animals have moral value, and can thus generate moral reasons in us.
However, even if we can have obligations towards animals, we do not always have these obligations. As defined above, an obligation only exists if the overwhelming weight of reasons favours a particular course of action. If the weight of reasons is not overwhelming, several courses of action may be equally morally permissible. And this can happen with animals as with anything -- as always in moral decision-making, context matters. Although I have promised to care for my cats, if I am forced to decide (by a mad philosopher) between my cats and my wife, I would be morally obligated to choose my wife. Although we are obligated to provide for an animal's well-being if we damage their habitat, we are not obligated to sacrifice significant well-being of humans to do so. (We would not, for example, be forced to tear down the houses built in the animal's former habitat and replant all the trees.)
Given this framework, it can be seen that, if the benefit is significant enough, it can provide reason to overwhelm our reasons for not harming animals that we have purchased. In other words, if there is great benefit in terms of knowledge or future medical technology to be gained from vivisection, then even though we have some reason not to harm the animals (because we did, after all, purchase them), this reason can be swamped by the former.
Which means, of course, that the question I suspended at the beginning -- the epistemological and scientific issue -- is actually the one that's going to decide the moral question in any particular situation.