Opening downlaods with unstuffit

Can anyone help me, I have recently purchased Absynth 2, but to get it working properly I had to download stuff from their website, I have done this but there is no default to open them with! I sent an e-mail to their tec support asking about this and they told me that there should be something called "Unstuffit" that should be set on default when I click on it, instead it asks me what I want to open them with I have searched and cannot find "Unstuffit". Is there a download on this website for this or has it another name?

Also is there a real tec support e-mail address or do we have to rely on this discussion board??

Regards Matt