I hope the title of the question wasn't too confusing. Basically here's what I'm trying to do...

I'm writing several hundred letters which all have the same content but with certain parts that are going to need to be specific to each recipient (ie: name, address, etc).

I'd like to create a form entry system with options for Name, address, etc, etc and will insert this into into different fields in my letter and give me the ability to easily input the data and print the several hundred versions of the same letter out on my printer, without having to manually type in the data into the document.

I apologize if this has already been answered, I wasn't sure exactly what tool or method to search for.