You don't save as in XHTML. You code in XHTML and save it as a .htm/.html page.
XHTML is easy to learn. If you've learnt HTML, XHTML will be a breeze. It's virtually HTML with a few minor changes.
You can use Dreamweaver to help you code in XHTML. Don't know about any other HTML editors.
Or, you can do a rjensen11 and code it in Notepad and then change the file extension from .txt to .htm.