Free Will is a difficult subject to discuss since different people put different meanings into the concept itself (and since tricky metaphysical issues often arise).
Basically there are two basic kinds of definitions of the concept, one that implies incompatibilism (that is, that Free Will and determinism are incompatible) and one that implies compatibilism.
The first one is concerned with the person's relation to the world around him and somehow demands that the person in all his actions introduce a new "cause" into the world, something that simply isn't a result of all the little forces working on him or her. Given this definition, if determinism is true there can be no Free Will. Some argue that quantum mechanics may give room for this kind of Free Will, while others (myself included) don't think that that will work either.
The second is concerned with the person's experience of the world and his own actions, and demands that the person's actions are in accordance with his decisions. Given this definition, it doesn't matter at all if the world is deterministic or not. Unless you, as percieved by yourself, perform actions that doesn't conform to your decisions, you have Free Will.
(Personally I've never understood why so many people think that the first kind of Free Will is important. How can it be, if I can't even tell if I have it or not? Clearly I have the second kind, and that's what important to me as a sentient being.)