While back, we posted a full how to guide to enable HD video recording by logging into your device using Open SSH and some compatible steps. Whatever, there's a tweak available in Cydia now to enable HD video recording with only one step.
To enjoy this tweak, your iPhone 3GS must be jailbroken, you can use our guide posted here to jailbreak your device on iOS 4.1 using Limera1n. Once your device is jailbroken, tap on Cydia and search for HD Video Enabler for 3GS under BigBoss repository then activate it from Winterboard app. This will allow you to enable HD video recording on your iPhone 3GS.