Here is the link and the step by step instructions are there...
http://androidforums.com/all-things-root-behold-2/54769-port-galaxy-1-6-behold-2-a.html
I did the BH_MAN_DONUT_R1.zip but they did update the Rom recently so the most up to date one currently is BH_MAN_DONUT_R2.zip and you can download the file at the link
As far as backing up your phone goes there are certain apps you can download that will save the apps and files you have now to the Micro SD card in your phone, I use ATrackDog(SD), Astro, and App Manager.
Just about anyone in the All things root behold 2 forum should be able to help you out with any other questions you may have.