Sorry, but iOS 5.1 has no jailbreak available. The only iOS 5 versions with an available jailbreak are 5.0.1 and 5.1.1.
Then I'm afraid that if you ever want to jailbreak, you will have to update to iOS 6 and wait for the release of an iOS 6 jailbreak. There never was and never will be a jailbreak for iOS 5.1. Here is the official iOS 6 jailbreak status thread, keep an eye on it. Any news about a jailbreak for iOS 6 will be announced here. http://www.ipadforums.net/ipad-hacking/89458-official-ios6-jailbreak-status-thread.html