I have a folder that I want to back-up to an external hard drive. Anytime I write new data to this folder, I want a copy sent to the HD. I have found a batch file to do just about everything...but this. Maybe I'm overlooking one...maybe this isn't possible? Have no experience with these...just had someone tell me that this could possibly work. Thanks ahead of time for any advise or references!

You can't run a batch file like that, because what you are looking for would be something that runs continuously in the background and copies data.
You can either purchase a program that will do this. Write a batch file that copies over everything (or certain timies/dates) at a specified time. Or else look into things like mirroring your drive (this makes a duplicate on the other drive).
If you are looking at backing up data I'd suggest writing a batch file that copies everything on Day1 into a folder called Day1, and on Day3 it copies everything into a folder called Day3 (and etc..), then use Scheduler to schedule this batch file to run when you want it to (or execute it manually)...