Very doable and not overly difficult. It will however require a lot of work and depending on your choice of compnents it could get expensive. You will need a front axle, a new tranny (maybe), a transfer case, 2 new drivelines, and the hardware to attatch all of them. What engine do you have? What transmission do you have?
Now the important part. What kind of truck are you building? Do you want a daily driver 4wd? Do you want a mild off-roader? Do you want an extreme mud machine? Do you want a rock crawler? You need to sit down and decide what you want your truck to be capable of, because this will determine the components that you will need to use in the build.
I will check back on your post to see what you are after and offer more advice, 4x4's have a special place in my automotive heart. My advice would be to sit down with a beverage of your choice and a piece of paper and decide what you want to be able to do and then you can begin piecing together the truck on paper and then do the fun part of putting it together for real. Good Luck.
Kyle
