Open iTunes, and navigate to your iPad 1. Hold the Shift key on your keyboard, and press "Restore". Select the iPad1,1_5.1.1_9B206_Restore.ipsw file that you downloaded. Wait for the restore to complete, and the iPad 1 to reboot. Plug your iPad
The blog contains uses for both non-jailbroken and jailbroken devices, how to jailbreak, possible youtube fix, and a list of apps and games working for IOS 5.1.1.