Use iTunes to back up your iPad. Once you are SURE it's backed up, update your iPad (using iTunes) to 5.1.1. This will retain all apps purchased through the app store, pictures, movies, etc. It will remove any cydia apps (obviously).
Then download the latest version of Absinthe. In my opinion this is the easiest tool to jailbreak your device. It does not remove any data from the device, but simply adds Cydia to the homescreen. From there you can restore your iPad from the backup you made before re-jailbreaking and then you'll have to reinstall all of your tweaks from Cydia and put back all of your sources. It'd be wise to write down your installed packages and sources before doing all of this.
Cheers