You can find out everything you need to know here. http://www.ranger-forums.com/forumdisplay.php?f=34
There are countless number of threads from people who have done the swap. As far as how hard it is, just depends on all what you want to do. If you want the simplest swap. You will have to use the explorer transmission and awd transfer case. You will lose the ability to put the truck into 2wd and the gas mileage will be affected. Being as you have a 94, the swap isn't as simple as it is with a 98+ Ranger.
This article pretty much sums everything you need to know