Certainly!
Using the same server to host both live and dev sites
Set up a new virtual host using a different host name (e.g. dev.example.com.)
Copy the MODx installation folder to a new folder and point the dev virtual host to this new directory.
Backup your live database using mysqldump or phpMyAdmin, and restore it as a different name.
Using a separate physical dev server than your live
Grab a copy of the file system folders and compress them into a single archive using tar or zip.
Backup your database using mysqldump or phpMyAdmin.
Copy both the archive and the database dump over to your development server.
Unzip the file system archive and move it to wherever you want to on your development server.
Restore the database onto your dev MySQL server.
Configure Apache to point to the path where you restored the archive.
Common to both the above methods
Follow the instructions
here for Revo, or
here for Evo, to adjust the file system paths and database locations as necessary.
