I was able to download the 3.0 Build on my Windows Machine but do not know how to install it.
The name is:
iphone_os_3.0_gm_seed__iphone_3g__7a341.dmg.smi
In iTunes 8.2 I hold the Shift Key down while selecting Check for Updates and it brings up the dialog to search my disk drive. When I navigate to the folder it only show files with "*.ipsw" which does not match the file above.
Any idea how to install a ".smi" file on Windows iTunes 8.2?
To get it working on Windows, you'll need to download an app like PowerISO. Open up the .dmg file and then extract the .ipsw.
All you need to do then is a shift update as normal.... but make sure your device is registered on apples dev's website otherwise it wont be able to activate/work or something like that....!!!
BTW I don't know why yours has downloaded with .smi on the end???!!!