Quote Originally Posted by lonestarvero View Post
Anyone know what user/group are appropriate?
Yes: whatever user/group your PHP instance uses (and that's often determined by Apache).

Questions about configuring PHP and Apache and Operating System and File System permissions are best asked on websites devoted those topics.

As I said before, Zen Cart is merely the messenger, telling you that it's unable to open the files for writing purposes, and the filesystem along with PHP are sending back a failure response.