When you’re an Apple iPhone Developer running Windows, you will find that Apple posts its beta’s as DMG files (iphone_os_3.0_beta_3__iphone_3g__7a280f.dmg), which Windows doesn’t handle by default. You may need PowerISO to extract the IPSW file within it and feed it to your iTunes, holding the Shift key and clicking the Restore button in iTunes…
Remember that PowerISO doesn’t automatically register DMG files, so you have to manually start PowerISO and drag the DMG file into it, which will then give you the ability to extract the IPSW file. Happy hacking!
