If you have been trying to upgrade your iPhone, iPad, or iPod Touch to iOS 5, but are getting the troublesome 3002 or 3005 error, here is a solution that may work for you.

First download the firmware file from Apple using one of the following links:  iPhone 3GS, iPhone 4 GSM, iPhone 4 CDMA, iPad (1), iPad 2 WiFi, iPad 2 GSM, iPad 2 CDMA. [Please choose the iDevice you have]

After the download is complete, close iTunes and disconnect your iDevice from your computer.

Next you must copy the ipsw file you previously downloaded from above to the following location:

On Windows: %APPDATA%\Apple Computer\iTunes\iP{one|ad|od} Software Updates

On Mac: ~/Library/iTunes/iP{one|ad|od} Software Updates

Finally connect your iDevice to your computer, Open up iTunes, and click update.

Hopefully this works for you!