64 bit Windows will not run 16 bit programs. To run 16 bit apps, such as the old .com dos stuff, you need to use an emulator, such as DosBox.
edit: for small powerful command line editor you may want to try vim
It has many implementations. 16 bit Dos ones as well as 32 bit Windows. It's a port of the vi editor that I ran into on Linux. I started using it enough that I found myself rapidly jumping between command and edit mode without having to think about it. I was afraid of going schizo. So I gave it up.
But it's way more powerful than Dos edit. You can rearrange whole paragraphs and make complex substitutions using a few commands that you can't do in free Windows editors I've seen. Most Windows editors that have similar capabilities cost $150 or more.
edit2: now that I look at the vim page again, seems it also comes in native 64 bit Windows versions.