In Apache (1.2 and up, I think), it's really easy, nest the following directives inside a Location or Directory directive:
<Files *.inc>
Deny from all
</Files>
In iPlanet server (former Netscape Enterprise Server), you can do it with ACLs or with obj.conf, there's no Files-directive to use in .htaccess which could handle the task as easily as in Apache. I'm not sure about these, but you can try them out.
Doing it with a single line in obj.conf: (I have no idea if this works!)
PathCheck fn="deny-existence" path="path/to/the/directory/*.inc"
In an ACL file, it would be: (more likely to work)
acl "*.inc"
deny absolute (all)
user = "anyone";
...and also require a line in the obj.conf :
<Object ppath="*.inc">
PathCheck fn="check-acl"
</Object>
...and the ACL file should be defined in magnus.conf:
ACLFile /path/to/the/file.acl
-j