Please refer to this article on Jailbreaking as this one is now outdated:
This is a Tethered Jailbreak of iOS 5 Final (Public Release) with RedSn0w 0.9.9b3 which works With iPod Touch G3, G4, iPhone 4, iPhone 3GS, iPad 1.
This video tutorial shows you how to jailbreak the public final release of iOS 5. This is for Mac but the same principal will work on Windows.
Please do this with caution and realize that this is a Tethered Jailbreak, so backup your device and make sure all your photos, videos, contacts, podcasts and music are synching from iTunes.
For RedSn0w download visit: http://www.idownloadblog.com/iphone-downloads/