If you are using Windows, you can select two separate documents and display them side by side. This does not synchronize the scrolling between windows, but you probably wouldn't want that anyway. If the content in one window surpasses the length of the content in the other, then you would need to scroll in each separately.
I am using Windows 7, and I can open two documents of the same type, do a Shift-right click on their icon at the bottom of the screen, and then choose the option to "Show windows side by side". I don't remember the exact steps for earlier versions of Windows, but I know they are very similar. This will allow you to use the editor of your choice and keep each screen positioned where you need it so that you can easily move back and forth as needed.