The XAMP will install fresh copies of Apache, MySQL, and PHP. If you have already got an apache server running you should make sure to backup what you have for that server before going this route. After you backup you should also uninstall the current version of Apache before installing this newer one. If there are any problems you should be able to revert to your existing Apache install. You should not be making these types of updates on a live production server though, you should always get the configuration sorted and tested before deploying on your live server.
If you know that you have a valid SMTP server setup then the next thing to do would be to define the site in DW including the testing server. Once that is all done you will be able to create a new page and apply Universal Email to it.