From Where you can access iOS 5.1 Jailbreak then you have to read furthur more about it.
Apple iOS 5.1 Apps and Jailbreak Official Website : http://UltimateJailbreak.com
Apple Software Update iOS 5.1 Compatibility:
iPhone 4GSM Model
iPod Touch 3rd generation
iPod Touch 4th generation
The following steps will help you jailbreak your device on Apple iOS 5.1
Step 1: Go to www.apple.com and Download latest iTune v 10.2.1 and Update your device to Software Update 5.1
Step 2: Then go to http://UltimateJailbreak.com and Download iOS 5.0.1 Jailbreak for Mac or Windows
Step 3: Save the iOS 5.1 Jailbreak Tool on desktop and Run as Administration
Step 4: Select your device and click on jailbreak button.
Step 5: Let the application do its work and wait for the app to show "Jailbreak Complete!" message.