As for iPhone 3GS old bootroom, you can untethered jailbreak it. Unfortunately, currently Redsn0w 0.9.10b6 does not support A5 device like iPad 2 and iPhone 4s.
So for those who their devices using iOS 5.0.1, it's recommended not to update to 5.1 if you want to keep the untethered jailbreak utility. Anyway here is the download links based on your OS.
- Download Redsn0w 0.9.10B6 for Mac
- Download Redsn0w 0.9.10B6 for Windows (Run as administrator mode)
- And then semi untethered jailbreak iOS 5.1 on iPhone 4, 3GS, iPad 1 and iPod touch.