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OS 4 betas are for registered, paid-up, iPhone developers only. You can only develop on a Mac. Therefore Apple only spend resources on making the betas install correctly on a Mac.

That said a paid-up developer would have access to the notes that go with the current release that offer a method to backup beta 2 devices (and I suspect therefore install) on a Windows machine. As the OP does not know what this is it appears he is using illegally obtained software.
 
nevermind, I'll wait till the final release comes out. I don't want to risk breaking my phone.
 
As a developer with a dead mac, I've upgraded my iPhone using my Windows machine. Upgrade was ok.
 
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