to correct you squid, the shaft doesn't slide into the t-case, it is bolted onto a yoke. and if the bolt holes line up from the driveshaft to the transfer case, and the u-joints are the same, then there is no problem using it, as long as your slip shaft part of the shaft isn't too far in, or too far out when it's all bolted togehter, you'd want it right in the middle, or close to it.
also squid, you'll never understand mechanics, or much of anyhting if you let it intimidate you, embrace what you wanna learn, try it out, and if you screw up, have someone show you the right way as to how to fix what you screwed up, and how ot do it right in the first place, i know you're new, but 4 years ago i didnt know how change a water pump, and now im a mechanic by trade amazingly enough without any shcooling, all my trainign was first hand/fuck up/ figure it out. and that is the best way to learn imho.
-zach