I need to create a development environment on my server so that my
website changes can be previewed by my partner before I publish them.
My partner is in a different geographical location than I am so
pubishing to a local area won't work. How can I create a development
version of our website that is viewable online without having to edit
all the existing html files to refer to the development area?

Greetings Dakota43,

You might consider simply renaming your edited "preview" files and
posting them on the actual website.  You won't include any links to
those "preview" pages, and you can easily insert "robot no follow"
codes on the preview pages to prevent search engines from indexing
them.

Best regards,
journalist-ga

Renaming files might break your links, so I'd be sure there isn't
another simpler way first.

You might be able to put an entire copy of the site into a
subdirectory off of the main site.  This will work if you do not use
absolute URLs in your links.  If the main site is in the \html
directory, put your testing copy into a \html\test directory.  The
result is that the test verwsion would be at
http://www.mysite.com/test/ rather than http://www.mysite.com/

You might also be able to register a subdomain for your domain name. 
Exactly how will depend on your domain registrar or DNS service
provider.  The result is that you'd end up with a www.mysite.com and a
test.mysite.com which could each be set up differently.  If you don't
know exactly how to do this, your registrar or hosting service can
help.