All you need to do is remove anything that has anything to do with PHP from the httpd.conf file.
If you do this then you won't have PHP anywhere. I think what he wants is to have some dirs have PHP, and some dirs to not have it.
I personally have never done it, but I believe it can be done using a directory objective to load the php stuff.
Try taking all of the lines concerning PHP and putting them into a directory objective like this:
<Directory c:/path/to/dir/that/should/have_php>
LoadModule php4_module c:/php/sapi/php4apache.dll
AddModule mod_php4.c
DirectoryIndex index.php index.html
AddType application/x-httpd-php .php
</Directory>
You would need to do that for every dir you wanted to have PHP support. Like I said, I haven't actually tried this myself, but in theory it should work.
Let me know either way. I'm curious myself.