Inserting forms with a fixed length in word 2007

I'm at my wit's end here, i've searched everywhere on the internet and can't find an answer or even a tip on what exactly i'm trying to do

We have an agreement with a simple underline for users to write data in, and usually it is just printed off and the data filled in manually, I want to convert this document to use forms, but whenever i try to insert a form it screws up the formatting on the entire page

is there a way that i can create a fixed size of a form and insert it into my current document without destroying all the formatting that is already there?

any help ould be greatly appreciated